Optical lens apparatus and associated method

ABSTRACT

An apparatus and associated method for controlling the propagation constant of a region of focusing propagation constant in an optical waveguide. The method comprising positioning an electrode of a prescribed electrode shape proximate the waveguide. A region of focusing propagation constant is projected into the waveguides that corresponds, in shape, to the prescribed electrode shape by applying a voltage to the shaped electrode. The propagation constant of the region of focusing propagation constant is controlled by varying the voltage. Light of certain wavelengths passing through the region of focusing propagation constant has a variable focal length.

FIELD OF THE INVENTION

This invention relates to optical devices, and more particularly tooptical waveguide devices.

BACKGROUND OF THE INVENTION

In the integrated circuit industry, there is a continuing effort toincrease device speed and increase device densities. Optical systems area technology that promise to increase the speed and current density ofthe circuits. Optical lenses are optical devices that are configured tofocus light. It is known to focus light using optical devices. Forinstance, light flowing through Bragg gratings are known to focus on afocal point. Optical lenses can be discrete elements made from glass orclear plastic or alternatively can be formed from a semiconductormaterial, such as silicon.

Optical lenses, as with most optical devices, are susceptible to changesin such operating parameters as temperature, device age, devicecharacteristics, contact, pressure, vibration, humidity, etc. As such,the optical lenses are typically contained in packaging that maintainsthe conditions under which the optical devices are operating. Providingsuch packaging is extremely expensive. Even if such packaging isprovided, passive optical lenses may be exposed to slight conditionchanges. As such, the passive optical lenses perform differently underthe different conditions. For example, a lens will focus light todifferent focal length depending on the conditions, or may even notprecisely focus light. If the characteristics of a passive optical lensis altered outside of very close tolerances, then the optical lens willnot adequately perform its function. In other words, there is noadjustability to the passive optical lenses.

As such it would be desirable to provide an optical lens that canadjustably focus light. Additionally, it would be desirable to provide amechanism to compensate in optical lens for variations in the operatingparameters such as temperature and device age.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and associated methodfor controlling the propagation constant of a region of focusingpropagation constant in an optical waveguide. The method comprisingpositioning an electrode of a prescribed electrode shape proximate thewaveguide. A region of focusing propagation constant is projected intothe waveguide that corresponds, in shape, to the prescribed electrodeshape by applying a voltage to the shaped electrode. The propagationconstant of the region of focusing propagation constant is controlled byvarying the voltage. Light of certain wavelengths passing through theregion of focusing propagation constant has a variable focal length.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate the presently preferredembodiment of the invention, and, together with the general descriptiongiven above and the detailed description given below, serve to explainfeatures of the invention.

FIG. 1 shows a front cross sectional view of one embodiment of anoptical waveguide device including a field effect transistor (FET);

FIG. 2 shows a top view of the optical waveguide device shown in FIG. 1;

FIG. 3 shows a section view as taken through sectional lines 3—3 of FIG.2;

FIG. 4 shows a front cross sectional view of one embodiment of anoptical waveguide device including a metal oxide semiconductor capacitor(MOSCAP);

FIG. 5 shows a front view of another embodiment of an optical waveguidedevice including a high electron mobility transistor (HEMT);

FIG. 6 shows a graph plotting surface charge density and the phaseshift, both as a function of the surface potential;

FIG. 7 shows one embodiment of a method to compensate for variations intemperature, or other such parameters, in an optical waveguide device;

FIG. 8 shows another embodiment of a method to compensate for variationsin temperature, or other such parameters, in an optical waveguidedevice;

FIG. 9 shows a top view of another embodiment of optical waveguidedevice 100;

FIG. 10 shows a side cross sectional view of one embodiment of a ridgeoptical channel waveguide device;

FIG. 11 shows a side cross sectional view of one embodiment of a trenchoptical channel waveguide device;

FIG. 12 shows one embodiment of a wave passing though a dielectric slabwaveguide;

FIG. 13 shows a top view of another embodiment of an optical waveguidedevice from that shown in FIG. 2, including one embodiment of aprism-shaped gate array that provides for light deflection by theoptical device;

FIG. 14 shows a top cross sectional view of the waveguide of theembodiment of prism-shaped gate array of FIG. 13 including dotted linesrepresenting a region of changeable propagation constant. The solidlight rays are shown passing through the regions of changeablepropagation constant corresponding to the prism-shaped gate array;

FIG. 15, including FIGS. 15A to 15D, show side cross section views ofthe optical waveguide device of FIG. 13 or taken through sectional lines15—15 in FIG. 13, FIG. 15A shows both gate electrodes 1304, 1306 beingdeactivated, FIG. 15B shows the gate electrode 1304 being actuated asthe gate electrode 1306 is deactivated, FIG. 15C shows the gateelectrode 1304 being deactuated as the gate electrode 1306 is activated,and FIG. 15D shows both gate electrodes 1304 and 1306 being actuated;

FIG. 16 shows a top view of another embodiment of an optical waveguidedevice that is similar in structure to the optical waveguide deviceshown in FIG. 2, with a second voltage source applied from the sourceelectrode to the drain electrode, the gate electrode and electricalinsulator is shown partially broken away to indicate the route of anoptical wave passing through the waveguide that is deflected from itsoriginal path along a variety of paths by application of voltage betweenthe source electrode and gate electrode;

FIG. 17 shows another embodiment of an optical deflector;

FIG. 18 shows a top view of one embodiment of an optical switch thatincludes a plurality of the optical deflectors of the embodiments shownin FIGS. 14, 15, or 16;

FIG. 19 shows a top view of another embodiment of an optical switchdevice from that shown in FIG. 18, that may include one embodiment ofthe optical deflectors shown in FIGS. 14, 15, or 16;

FIG. 20 shows one embodiment of a Bragg grating formed in one of theoptical waveguide devices shown in FIGS. 1-3 and 5;

FIG. 21 shows another embodiment of a Bragg grating formed in one of theoptical waveguide devices shown in FIGS. 1-3 and 5;

FIG. 22 shows yet another embodiment of a Bragg grating formed in one ofthe optical waveguide devices shown in FIGS. 1-3 and 5;

FIG. 23 shows one embodiment of a waveguide having a Bragg grating ofthe type shown in FIGS. 20 to 22 showing a light ray passing through theoptical waveguide device, and the passage of reflected light refractingoff the Bragg grating;

FIG. 24 shows an optical waveguide device including a plurality of Bragggratings of the type shown in FIGS. 20 to 22, where the Bragg gratingsare arranged in series;

FIG. 25, which is shown exploded in FIG. 25B, shows a respective topview and top exploded view of another embodiment of an optical waveguidedevice including a gate electrode configured that may be configured asan Echelle diffraction grating or an Echelle lens grating;

FIG. 26 shows a top cross sectional view taken within the waveguide ofthe optical waveguide device illustrating the diffraction of opticalpaths as light passes through the actuated Echelle diffraction gratingshown in FIG. 25, wherein the projected outline of the region ofchangeable propagation constant from the Echelle diffraction grating isshown;

FIG. 27 shows an expanded view of the optical waveguide device biased tooperate as an Echelle diffraction grating as shown in FIG. 26;

FIG. 28 shows a top cross sectional view taken through the waveguide ofthe optical waveguide device illustrating the focusing of multipleoptical paths as light passes through the actuated Echelle lens gratingshown in FIG. 25, illustrating the region of changeable propagationconstant resulting from the Echelle lens grating;

FIG. 29 shows an expanded view of the optical waveguide device biased tooperate as an Echelle lens grating as shown in FIG. 28;

FIG. 30 shows a top view of one embodiment of an optical waveguidedevice that includes a Bragg grating, and is configured to act as anoptical lens;

FIG. 30A shows a top cross sectional view taken through the waveguide ofthe optical waveguide device shown in FIG. 30 illustrating light passingthrough the waveguide;

FIG. 31 shows a top view of another embodiment of optical waveguidedevice that includes a filter grating, and is configured to act as anoptical lens;

FIG. 31A shows a top cross sectional view taken through the waveguide ofthe optical waveguide device shown in FIG. 31 illustrating light passingthrough the waveguide;

FIG. 32 shows a top view of another embodiment of optical waveguidedevice that includes a Bragg grating, and is configured to act as anoptical lens;

FIG. 32A shows a top cross sectional view taken through the waveguide ofthe optical waveguide device shown in FIG. 32;

FIG. 33 shows a front view of another embodiment of optical waveguidedevice from that shown in FIG. 1;

FIG. 34 shows a top view of one embodiment of an arrayed waveguide (AWG)including a plurality of optical waveguide devices;

FIG. 35 shows a schematic timing diagram of one embodiment of afinite-impulse-response (FIR) filter;

FIG. 36 shows a top view of one embodiment of an FIR filter;

FIG. 37 shows a schematic timing diagram of one embodiment of aninfinite-impulse-response (IIR) filter;

FIG. 38 shows a top view of one embodiment of an IIR filter;

FIG. 39 shows a top view of one embodiment of a dynamic gain equalizerincluding a plurality of optical waveguide devices;

FIG. 40 shows a top view of another embodiment of a dynamic gainequalizer including a plurality of optical waveguide devices;

FIG. 41 shows a top view of one embodiment of a variable opticalattenuator (VOA);

FIG. 42 shows a top view of one embodiment of optical waveguide device100 including a channel waveguide being configured as a programmabledelay generator 4200;

FIG. 43 shows a side cross sectional view of the FIG. 42 embodiment ofprogrammable delay generator 4200;

FIG. 44 shows a top view of one embodiment of an optical resonator thatincludes a plurality of optical waveguide devices that act as opticalmirrors;

FIG. 45 shows a top cross sectional view taken through the waveguide ofthe optical resonator shown in FIG. 44;

FIG. 46 shows a top view of one embodiment of an optical waveguidedevice configured as a beamsplitter;

FIG. 47 shows a top view of one embodiment of a self aligning modulatorincluding a plurality of optical waveguide devices;

FIG. 48 shows a top view of one embodiment of a polarizing controllerincluding one or more programmable delay generators of the type shown inFIGS. 42 and 43;

FIG. 49 shows a top view of one embodiment of an interferometerincluding one or more programmable delay generators of the type shown inFIGS. 42 and 43; and

FIG. 50 shows a flow chart of method performed by the polarizationcontroller shown in FIG. 48.

DETAILED DESCRIPTION OF THE EMBODIMENT

The present disclosure provides multiple embodiments of opticalwaveguide devices in which light travels within a waveguide. Differentembodiments of optical waveguide devices are described that performdifferent functions to the light contained in the waveguide. Alteringthe shape or structure of an electrode(s) can modify the function of theoptical waveguide device 100.

There are a variety of optical waveguide devices 100 that are describedin this disclosure. Embodiments of optical waveguide devices include awaveguide located in a Field Effect Transistor (FET) structure as shownin FIGS. 1 to 3; a waveguide associated with metal oxide semiconductorcapacitor (MOSCAP) structure is shown in FIG. 4; and a waveguide locatedin the High Electron Mobility Transistor (HEMT) as shown in FIG. 5. InMOSCAPs, one or more body contact(s) is/are separated from the gateelectrode by a semiconductor waveguide and an electrical insulator. Inthe embodiment of FETs applied to the present invention, a substantiallyconstant potential conductor is applied between the source electrode andthe drain electrode to maintain the two electrodes at a common voltage.When the source electrode of a FET is held at the same potential as thedrain electrode, the FET functionally operates as, and may be consideredstructurally to be, a MOSCAP. To make the description for the aboveembodiments more uniform, the term “body contact electrodes” is used todescribe either the body contact at the base of the MOSCAP or thesubstantially common potential source electrode and drain electrode inthe FET.

The application of the voltage between the gate and body contact(s)predominantly changes the distribution of free-carriers (eitherelectrons or holes) near the semiconductor/electrical insulatorboundary. These essentially surface localized changes in the freecarrier distributions are referred to as two-dimensional electron gas or2DEG included in MOSCAPs. In a FET structure, for example, an increasein the application of the bias leads consecutively to accumulation ofcharges (of the same type as the semiconductor i.e. holes in a p-typeand electrons in n-type, depletion, and finally inversion. In 2DEGs, thepolarity of semiconductor is opposite the type of the predominant freecarriers, i.e. electrons in p-type or holes in n-type). In a HighElectron Mobility Transistor (HEMT), the electron (hole) distributionformed just below the surface of the electrical insulator is referred toas 2DEG because of particularly low scattering rates of charge carriers.At any rate, for the purposes of clarity, all of the above shall bereferred to as 2DEG signifying a surface localized charge density changedue to application of an external bias.

The term “semiconductor” is used through this disclosure in particularreference to the waveguides of the particular optical waveguide devices.The semiconductor waveguide is intended to represent a class ofsemiconductor materials. Silicon and Germanium are natural singleelement semiconductors at room temperature. GaAs and InP are examples ofbinary compound semiconductors. There are semiconductors made from threeelement semiconductors such as AlGaAs. The salient feature of allsemiconductors is the existence of a band-gap between the valence andthe conduction band. Multiple layers of semiconductors may also be usedin the construction of a waveguide as well as to create an opticalwaveguide device including a MOSCAP, a FET, or a HEMT. For the purposeof this disclosure, the semiconductor provides the ability to controlthe density of the 2DEG by the application of the gate voltage. Anydescription of a specific semiconductor in this disclosure is intendedto be enabling, exemplary, and not limiting in scope. The conceptsdescribed herein are intended to apply to semiconductors in general.

These concepts relating to the optical waveguide device apply equallywell to any mode of light within a waveguide. Therefore, different modesof light can be modulated using multi-mode waveguides. The physicalphenomena remains as described above for multi-mode waveguides.

I. Optical Waveguide Device

The embodiments of optical waveguide device 100 shown in multiplefigures including FIGS. 1-3, and 5, etc. include a field effecttransistor (FET) portion 116 that is electrically coupled to a waveguide106. One embodiment of the waveguide is fabricated proximate to, andunderneath, the gate electrode of the FET portion 116. The waveguide istypically made from silicon or another one or plurality of III-Vsemiconductors. The FET portion 116 includes a first body contactelectrode 118, a gate electrode 120, and a second body contact electrode122. A voltage can be applied by e.g., a voltage source 202 to one ofthe electrodes. The gate electrode 120 is the most common electrode inwhich the voltage level is varied to control the optical waveguidedevice.

The variation in voltage level changes the propagation constant of atleast a portion of the waveguide 106. The changes in the index profileof the waveguide are determined by the location and shapes of all theelectrodes. The density of the 2DEG generally follows the shape of thegate electrode 120. Therefore, the shape of the gate electrode may beconsidered as being projected into a region of changeable propagationconstant 190 (the value of the propagation constant may vary atdifferent locations on the waveguide 106). The region of changeablepropagation constant 190 is considered to be that region through theheight of the waveguide in which the value of the propagation constantis changed by application of voltage to the gate electrode 120. Gateelectrodes 120 are shaped in non-rectangular shapes (as viewed fromabove or the side depending on the embodiment) in the differentembodiments of optical waveguide device. The different embodiments ofthe optical waveguide device perform such differing optical functions asoptical phase/amplitude modulation, optical filtering, opticaldeflection, optical dispersion, etc. Multiple ones of the opticalwaveguide devices can be integrated into a single integrated opticalcircuitry as an arrayed waveguide (AWG), a dynamic gain equalizer, and alarge variety of integrated optical circuits. Such optical waveguidedevices and integrated optical circuits can be produced using largelyexisting CMOS and other semiconductor technologies.

FIGS. 1 to 3 will now be described in more detail, and respectively showa front, top, and side view of one embodiment of an optical waveguidedevice 100. FIG. 1 shows a planar semiconductor waveguide bounded bylow-index insulating materials to which the light is coupled using aprism coupler 112. Other well-known types of coupling include gratings,tapers, and butt-coupling that are each coupled to the end of thewaveguide. The “gate” electrode 120 is positioned directly above thelight path in the semiconductor waveguide. The gate electrode isseparated from the semiconductor by the low-index dielectric acting asan electrical insulator. The body contact electrodes are electricallycoupled to the semiconductor. This embodiment may be considered to be aFET structure with the body contact electrodes 118, 122 forming asymmetric structure typically referred to as “source” and “drain” in FETterminology. A substantially constant potential conductor 204 equalizesthe voltage level between the first body contact electrode 118 and thesecond body contact electrode 122. The first body contact electrode andthe second body contact electrode can thus be viewed as providingsymmetrical body contact electrodes to the semiconductor. In anotherembodiment, the body contact is placed directly underneath the lightpath and underneath the waveguide.

In yet another embodiment, the body contact is positioned symmetricallylaterally of both sides of, and underneath, the incident light pathwithin the waveguide. The body contact in each of these embodiments isdesigned to change a free-carrier distribution region in a twodimensional electron gas (2DEG) 108 near the semiconductor/electricalinsulator boundary of the waveguide along the light travel path. Thischange in free-carrier distribution results from application of thepotential between the insulated gate electrode and the one or pluralityof body contact electrodes connected to the body of the semiconductor.

The FIG. 1 embodiment shows the optical waveguide device 100 includingan integrated field effect transistor (FET) portion 116. The fieldeffect transistor (FET) portion 116 includes the gate electrode 120, thefirst body contact electrode 118, and the second body contact electrode122, but the channel normally associated with a FET is either replacedby, or considered to be, the waveguide 106. Examples of FETs that can beused in their modified form as FET portions 116 (by using the waveguideinstead of the traditional FET channel) include ametal-oxide-semiconductor FET (MOSFET), a metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor FET(MESFET), a modulation doped FET (MODFET), a high electron mobilitytransistor (HEMT), and other similar transistors. In addition, ametal-oxide-silicon capacitor (MOSCAP) may also be similarly modified toform a FET portion.

FIGS. 1, 2, and 3 shows one embodiment of optical waveguide device 100that includes a substrate 102, a first electrical insulator layer 104, awaveguide 106, a first body contact well 107, a second body contact well109, the 2DEG 108, a second electrical insulator layer 110, an inputprism 112, an output prism 114, and the field effect transistor (FET)portion 116. The 2DEG 108 is formed at the junction between the siliconwaveguide 106 and the second electrical insulator layer 110 of thewaveguide 106. Multiple embodiments of optical waveguide devices aredescribed that, upon bias of the gate electrode 120 relative to thecombined first body contact electrode 118 and second body contactelectrode 122, effect the passage of light through the waveguide 106 toperform a variety of functions.

The FIG. 12 embodiment of semiconductor waveguide (which may be doped)106 has a thickness h, and is sandwiched between the first electricalinsulator layer 104 and the second electrical insulator layer 110. Thefirst electrical insulator layer 104 and the second electrical insulatorlayer 110 are each typically formed from silicon dioxide (glass) or anyother electrical insulator commonly used in semiconductors, for exampleSiN. The electrical insulator layers 104, 110 confine the light usingtotal internal reflection of the light traversing the waveguide 106.

Light is injected into the waveguide 106 via the input prism 112 andlight exits from the waveguide 106 via the output prism 114, althoughany light-coupling device can be used to respectively inject or removethe light from the waveguide 106. Examples of light-coupling devicesinclude prisms, gratings, tapers, and butt-couplings. Light passing fromthe input prism (or other input port) to the output prism (or otheroutput port) follows optical path 101 as shown in FIG. 1. The opticalpath 101 may be defined based upon the function of the optical waveguidedevice 100. For example, if the optical waveguide device functions as anoptical modulator, optical deflector, or an optical filter, the opticalpath 101 can be respectively considered to be an optical modulationregion, an optical deflection region, or an optical filtering region,etc.

As described earlier, application of voltage on the gate electrode 120relative to the combined first body contact electrode 118 and secondbody contact electrode 122 leads to a change in the propagation constantvia changes induced in the free-carrier density distribution 108. In aMOSCAP, the capacitance of the device is controlled by the voltage dueto presence (or absence) of 2DEG. In case of a FET, changes in the freecarrier distribution also control the conductance between the first bodycontact electrode and the second body contact electrode. Thefree-carriers are responsible for changing the optical phase or theamplitude of the guided wave depending on their density which in turn iscontrolled by the gate voltage. The basis of field-effect transistoraction, i.e., rapid change in 2DEG as a function of gate voltage, isalso responsible for the control of the light wave and enablesintegration of electronic and optical functions on the same substrate.Thus traditional FET electronic concepts can be applied to provideactive optical functionality in the optical waveguide device 100. TheFET portion 116 is physically located above, and affixed to, thewaveguide 106 using such semiconductor manufacturing techniques asepitaxial growth, chemical vapor deposition, physical vapor deposition,etc.

The propagation constant (and therefore the effective mode index) of atleast a portion of the waveguide in the optical waveguide device 100 ischanged as the free carrier distribution 108 changes. Such changing ofthe propagation constant results in phase modulation of the lightpassing through that device. The phase modulation occurs in a regions ofchangeable propagation constant, indicated in cross-hatching in FIGS. 1and 3 as 190, that closely follows the two-dimensional planar shape ofthe gate electrode through the height of the waveguide to form a threedimensional shape.

FIG. 2 shows one embodiment of a voltage source configuration thatbiases the voltage of the optical waveguide device 100 by using avoltage source 202 and a substantially constant potential conductor 204.The substantially constant potential conductor 204 acts to tie thevoltage level of the first body contact electrode 118 to the voltagelevel of the second body contact electrode 122. The voltage source 202biases the voltage level of the gate electrode 120 relative to thecombined voltage level of the first body contact electrode 118 and thesecond body contact electrode 122.

To apply a voltage to the gate electrode, a voltage source 202 appliesan AC voltage v_(g) from the gate electrode 120 to the combined firstbody contact electrode 118 and second body contact electrode 122. The ACvoltage v_(g) may be configured either as a substantially regular (e.g.sinusoidal) signal or as an irregular signal such as a digital datatransmission. In one embodiment, the AC voltage v_(g) may be consideredas the information carrying portion of the signal. The voltage source202 can also apply a DC bias V_(g) to the gate electrode 120 relative tothe combined first body contact electrode 118 and second body contactelectrode 122. Depending on the instantaneous value of the V_(g), theconcentration of the 2DEG will accumulate, deplete, or invert as shownby the different regions in FIG. 6. In one embodiment, the DC bias V_(g)is the signal that compensates for changes in device parameters. Thecombined DC bias V_(g) and AC voltage v_(g) equals the total voltageV_(G) applied to the gate electrode by the voltage source 202. It willbe understood from the description above that modulation of v_(g) canthus be used to effect, for example, a corresponding modulation of lightpassing through the waveguide 106.

The voltage potential of the first body contact electrode 118 is tied tothe voltage potential of the second body contact electrode 122 by thesubstantially constant potential conductor 204. Certain embodiments ofthe substantially constant potential conductor 204 include a meter 205(e.g. a micrometer) to measure the electrical resistance of the gateelectrode from the first body contact electrode to the second bodycontact electrode. The term “substantially” is used when referring tothe constant potential conductor because the meter 205 may generate somerelatively minor current levels in comparison to the operating voltageand current levels applied to the optical waveguide device. The minorcurrent levels are used to measure the resistance of the gate electrode.The current level produced by the meter is relatively small since thevoltage (typically in the microvolt range) of the meter is small, andthe waveguide resistance is considerable (typically in the tens ofohms).

The electrical resistance of the gate electrode is a function of suchparameters as gate voltage, temperature, pressure, device age, anddevice characteristics. As such, the voltage (e.g. the AC voltage or theDC voltage) applied to the gate electrode can be varied to adjust theelectrical resistance of the gate electrode to compensate for suchparameters as temperature, pressure, device age, and/or devicecharacteristics. Therefore, the voltage applied to the gate electrodecan be adjusted to compensate for variations in the operating parametersof the optical waveguide device.

As the temperature of the optical waveguide device varies, the DC biasV_(g) applied to the gate electrode 120 of the optical waveguide deviceis adjusted to compensate for the changed temperature. Other parameters(pressure, device age, device characteristics, etc.) can be compensatedfor in a similar manner as described for temperature (e.g. using apressure sensor to sense variations in pressure). This disclosure is notlimited to discussing the sensing and compensating for temperature sincethe other parameters can be compensated for in a similar manner.Different meter 205 and/or controller 201 embodiments may be provided tocompensate for the different temperatures.

FIG. 7 shows an embodiment of method 700 that compensates fortemperature variations in an optical waveguide device. The method 700starts with step 702 in which the temperature sensor 240 determines thetemperature of the optical waveguide device. The temperature sensor 240can be located either on the substrate or off the substrate. Thetemperature sensor inputs the temperature determined by the temperaturesensor to the controller 201 in step 703. The method 700 continues tostep 704 in which the DC bias V_(g) that is applied to the gateelectrode is adjusted to compensate for variations in the temperature.The controller 201 includes stored information that indicates therequired change in DC bias ΔV_(g) that is necessary to compensate forvariations in temperature, for each value of DC bias V_(g) for eachtemperature within the operating range of the optical waveguide device.The method 700 continues to step 706 in which the AC voltage v_(g) isapplied to operate the optical waveguide device as desired in thewaveguide.

The amount of AC voltage v_(g) is then superimposed on the DC bias V_(g)that is applied to the gate electrode to provide for the desiredoperation of the optical waveguide device 200 (e.g. the voltagenecessary for optical modulation, optical filtering, optical focusing,etc.). The AC voltage v_(g) superimposed on the combined DC bias V_(g)and the DC bias change ΔDC yields the total signal V_(G) applied to thegate electrode.

Another embodiment of compensation circuit, that compensates for thechange in temperature or other operating parameter(s) of the opticalwaveguide device, measures the electrical resistance of the gate betweenthe first body contact electrode 118 and the second body contact 122.The electrical resistance of the waveguide is a function of temperature,device age, device characteristics, and other such parameters. The meter205 measures the electrical resistance of the waveguide. For a givenwaveguide, the same resistance corresponds to the same electron densityand the same hole density in the waveguide. Therefore, if the sameelectrical resistance of the waveguide is maintained, the opticalwaveguide will behave similarly to cause a similar amount of suchoptical action as optical modulation, optical filtering, opticalfocusing, or optical deflection.

FIG. 8 shows another method 800 used by the controller 201 to compensatefor temperature variations of the optical waveguide device. The method800 starts with step 802 in which the meter 205 measures the electricalresistance of the waveguide. The method 800 continues to step 804 inwhich the measured electrical resistance of the waveguide is transferredto the controller 201. The method continues to step 806 in which thecontroller applies the amount of DC bias V_(g) required to be applied tothe gate electrode for that particular value of electrical resistance ofthe waveguide. Such parameters as temperature and device age thattogether may change the electric resistance of the waveguide can thus becompensated for together. Therefore, after measuring the electricalresistance of the waveguide, a feedback loop applies the voltage forthat measured resistance. The method 800 continues to step 808 in whichthe AC voltage v_(g) is applied to operate the optical waveguide device(i.e. modulate, filter, focus, and/or deflect light) as desired in thewaveguide.

In both of these temperature compensating embodiments shown in FIGS. 7and 8, the controller 201 allows the DC bias V_(g) to drift slowly asthe temperature varies to maintain the average resistance of thewaveguide from the source electrode to the drain electrode substantiallyconstant. These temperature-compensating embodiments make the opticalwaveguide device exceedingly stable. As such, the required complexityand the associated expense to maintain the temperature and otherparameters over a wide range of temperature are reduced considerably.

Suitably changing the voltages applied between the gate electrode 120,and the combined first body contact electrode 118 and second bodycontact electrode 122 results in a corresponding change in the freecarrier distribution in the 2DEG 108. In the FIG. 1 embodiment ofoptical waveguide device 100, altering the voltage applied to the gateelectrode 120 of the FET portion 116 changes the density of freecarriers in the 2DEG 108. Changing free carriers distribution in the2DEG 108 changes the effective mode index of the 2DEG 108 in thewaveguide. Changing the free carrier distribution similarly changes theinstantaneous propagation constant level of the region of changeablepropagation constant 190 (e.g., the area generally underneath the gateelectrode 120 in the FIG. 1 embodiment) within the waveguide 106.

Effective mode index, and equivalently propagation constant, bothmeasure the rate of travel of light at a particular location within thewaveguide taken in the direction parallel to the waveguide. For a lightbeam traveling over some distance in some medium at a velocity V, thevelocity V divided by the speed of light in vacuum is the index for thatmedium. Glass has a propagation constant of 1.5, which means lighttravels 1.5 times slower in glass then it does in a vacuum. For thesilicon in the waveguide the propagation constant is about 3.5. Since aportion of the light path travels in silicon and part of the light pathis in the glass, the propagation constant is some value between 1.5 and3.5. Therefore, the light is travelling at some effective speed measuredin a direction parallel to the axial direction of the waveguide. Thatnumber, or speed, is called effective index of the waveguide. Each modeof light has a distinct effective index (referred to as the effectivemode index) since different modes of the waveguide will effectivelytravel at different speeds.

The effective mode index is the same thing as the propagation constantfor any specific mode of light. The term effective mode index indicatesthat the different modes of light within a waveguide travel at differentvelocities. Therefore there are a plurality of effective indexes for amulti-mode waveguide, each effective index corresponds to a differentmode of light. The propagation constant (or the effective index)measures the average velocity for a phase of light for specific modetravel parallel to the axis of the waveguide as shown in FIG. 12. Thepropagation constant multiplied by the length would indicate how long ittakes to go that length. Through this disclosure, the effective indexfor a mode (the effective mode index) is considered to be the samemeasure as the propagation constant for that mode of light. The termpropagation constant is primarily used throughout the remainder of thedisclosure for uniformity.

Changing the propagation constant of the waveguide 106 by varying the2DEG 108 can phase modulate or amplitude modulate the light in thewaveguide. Within the waveguide, the degree of modulation is local inthat it depends on the density of 2DEG at a particular location. Theshape of the electrode, or other arrangements of body contactelectrodes, can impose a spatially varying phase or amplitude pattern tothe light beam in the waveguide. This in turn can be used to accomplisha wide variety of optical functions such as variable attenuators,optical programmable filters, switches, etc. on the optical signalsflowing through the waveguide 106.

A controller 201 controls the level of the total voltage V_(G) appliedto the voltage source 202. The optical waveguide device 100 can beemployed in a system that is controlled by the controller 201, that ispreferably processor-based. The controller 201 includes a programmablecentral processing unit (CPU) 230 that is operable with a memory 232, aninput/output (I/O) device 234, and such well-known support circuits 236as power supplies, clocks, caches, displays, and the like. The I/Odevice receives, for example, electrical signals corresponding to adesired modulation to be imposed on light passing through the waveguide106. The controller 201 is capable of receiving input from hardware inthe form of temperature sensors and/or meters for monitoring parameterssuch as temperature, optical wavelength, light intensity, devicecharacteristics, pressure, and the like. All of the above elements arecoupled to a control system bus to provide for communication between theother elements in the controller 201 and other external elements.

The memory 232 contains instructions that the CPU 230 executes tofacilitate the monitor and control of the optical waveguide device 100.The instructions in the memory 232 are in the form of program code. Theprogram code may conform to any one of a number of different programminglanguages. For example, the program code can be written in C, C++,BASIC, Pascal, or a number of other languages. Additionally, thecontroller 201 can be fashioned as an application-specific integratedcircuit (ASIC) to provide for quicker controller speed. The controller201 can be attached to the same substrate as the optical waveguidedevice 100.

In the FIG. 1 embodiment of waveguide 106, electrons (hole) concentratein the waveguide to form the 2DEG 108 that forms a very narrow channelnear the boundary of the silicon waveguide 106 and the second electricalinsulator layer 110. The surface inversion charge density q_(n) in the2DEG 108 is a direct function of the local surface potential φ_(s)applied to the waveguide 106. The local surface potential φ_(s) is, inturn, directly related to the total instantaneous voltage on the gateelectrode 120. The total voltage of light in the waveguide V_(G)satisfies the equation V_(G)=V_(g)+v_(g), where V_(g) is the DC bias andv_(g) is the AC bias. The local surface potential φ_(s) is a function ofthe total voltage V_(G), and is given by the equations: $\begin{matrix}{{\phi_{s} = {\frac{Q}{C} + V_{G} + \frac{Q_{O\quad X}}{C_{O\quad X}} + \phi_{m\quad s}}}{\phi_{s} \equiv {\frac{Q}{C} + V_{G}^{\prime}}}} & 1\end{matrix}$

The total potential V_(G) that is applied to the waveguide 106 is thus afactor of the effective capacitance C of the optical waveguide device100. The effective capacitance C itself depends on the distribution ofthe free-carriers. Thus, the capacitance in the MOS like device is afunction of the applied voltage. The charges Q and capacitance C in theequation 1 above are measured per unit area. Since the 2DEG densitydepends only on φ_(s), dopant density, and temperature; 2DEG densityq_(n) can be plotted vs. φ_(s). FIG. 6 illustrates a curve 602 thatplots surface charge density as a function of surface potential for anSi/SiO₂ MOSCAP where the uniform dopant density is assumed to be 10¹⁶cm⁻² at room temperature. FIG. 6 also shows curve 604 that plots phaseshift that is applied to the optical wave passing through waveguide 106for a 3 mm long rectangular gate region. The phase shift is plotted as afunction of surface potential φ_(s).

A side view of one embodiment of the optical waveguide device includinga waveguide located in a MOSCAP is shown in FIG. 4. The opticalwaveguide device includes a MOSCAP 400 including a body contact 402, awaveguide 106, an electric insulator layer 405, and a gate electrode406. In the embodiment of MOSCAP similar to as shown in FIG. 4, avoltage source 410 applies a voltage between the gate electrode 406 andthe body contact 402 to alter a level of propagation constant in aregion of changeable propagation constant 190 within the waveguide 106.The variations to the effective mode index and the propagation constantresult occur similarly to in the FET embodiments of optical waveguidedevice 100 as described below.

In the MOSCAP embodiment of optical waveguide device shown in FIG. 4,the body contact 402 is positioned below the waveguide 106.Alternatively, body contacts may be located where the traditional sourceand drain electrodes exist on traditional FETs. The body contact in theFET embodiment of optical waveguide device shown in FIGS. 1 to 3 isformed from the first body contact electrode being electrically coupledat the same potential as the second body contact electrode. Applicationof the electric field due to the potential difference between the “gate”and the body contacts results in changes in the distribution of freecharges as shown in the embodiment of FIG. 4.

FIG. 5 discloses one embodiment of high electron mobility transistor(HEMT) 500. The HEMT 500 comprises a semi-electric insulating substrate502, an undoped buffer waveguide layer 106, an undoped spacer layer 506,a doped donor layer 508, a 2DEG 505, the first body contact electrode118, the gate electrode 120, and the second body contact electrode 122.In one embodiment, the semi-insulating substrate 502 is formed fromAlGaAs. The undoped buffer waveguide layer 106 is formed from GaAs. Theundoped spacer layer 506 is formed from AlGaAs. The doped donor layer508 is formed from a doped AlGaAs.

During operation of the optical waveguide device, the 2DEG 505 increasesin height (taken vertically in FIG. 5) to approximately 20 angstroms.The 2DEG 505 is generated at the interface between the undoped spacerlayer 506 and the undoped buffer waveguide layer 106 as a result of thenegative biasing of the doped donor layer 508. Such negative biasingdrives the electron carriers in a 2DEG 505 generally downward, therebyforming a p-type 2DEG 505. Application of voltage to the gate electrodetends to increase the free carrier distribution in those portions of the2DEG 505 that are proximate the gate electrode. Such an increase in thefree carrier distribution in the 2DEG increases the effective mode indexin the waveguide 106 formed underneath the 2DEG 505. The gate electrode120 is formed having a prescribed electrode shape. The shape of theeffective mode index region within the waveguide 106 (i.e., the regionhaving an effective mode index that is changed by the application ofvoltage to the gate electrode) generally mirrors the shape of the gateelectrode 120 as viewed from above in FIG. 5. Additionally, the undopedspacer layer 506 acts as an insulative layer, to allow the formation ofthe 2DEG. HEMTs are formed in a variety of embodiments, several of whichare described in U.S. Pat. No. 6,177,685 to Teraguchi et al. that issuedon Jan. 23, 2001 (incorporated herein by reference in its entirety).

From semiconductor physics, the change in the distribution of freecharges is most pronounced near the electrical insulator-semiconductorboundary. These changes in the free-carrier distribution change theindex profile of the optical waveguide from a well-known relationship inplasma physics given by the Drude Model. The change in the free carrierdistribution changes the propagation constant of the optical waveguidedevice from a well-known relationship in plasma physics given by theDrude model in a region of changeable propagation constant 190 withinthe waveguide. The changes in the free-carrier distribution induced inthe semiconductor by the application of electric fields between the gateelectrode and the body contact electrode(s) modulates the phase and/oramplitude of the optical wave passing through the region of changeablepropagation constant 190. Thus, local changes in the free carrierdistribution induced by a change in applied voltage to the gateelectrode are impressed on the local optical phase or the amplitude oflight passing through the waveguide. The shape of the chargedistribution, i.e., the region of changeable propagation constant 190,provides the appropriate optical function as described below. Inmultiple embodiments, the pattern of the gate electrode (i.e., theplanar shape of the gate) controls the shape of the free carrierdistribution. The change in free carrier distribution, in turn, changesthe local effective mode index, or propagation constant, of thewaveguide in the region of changeable propagation constant 190. The samephenomena of change in the refractive index profile of the waveguide maybe ascribed by indicating that group delay or the group velocity of thelight beam has been changed as the free carrier distribution varies.

Therefore, the effective mode index, the propagation constant, the groupdelay, or the group velocity relate to an equivalent concept, namely,parametizing changes in the waveguide's refractive index profile on theoptical beam passing through the region of changeable propagationconstant 190 in the waveguide. This principle applies to all embodimentsof optical waveguide devices, including those shown in FIGS. 1-3, 4, and5.

The relationship between the effective mode index, the propagationconstant, the group delay, or the group velocity apply to waveguides ofall thickness' is now considered. In the case of “thick” waveguides, thelight ray travels by bouncing between the two bounding planes defined bythe insulator layers 110 and 104. The light ray can be easilyidentified, typically using the concept of phase or amplitude changesthat are directly imposed on a beam that has directly undergone one ormultiple interactions with free carriers. However, the concepts ofeffective mode index, propagation constant, group delay, or groupvelocity signify the same final result on the light beam. In thisdisclosure, the terms propagation constant, effective mode index, groupdelay, and group velocity are each used to describe the effects ofchanges in the free-carrier distribution due to electric field appliedto a semiconductor in an optical waveguide device, whether the opticalwaveguide device uses FET, HEMT, MOSCAP, or any other type of opticalwaveguide device technology.

Controlling the 2DEG density provides the optical function of an opticalwaveguide device. As described, adjusting the gate voltage can controlthe 2DEG density. The density may be spatially varied to provide morecomplex functions. A triangular shaped density distribution (included ina region of changeable propagation constant) is capable of deflectingthe light beam in a fashion similar to a prism in ordinary optics. Anundulating pattern of 2DEG of a particular spatial period canreflect/deflect a specific wavelength to form a Bragg grating. The exactshape or the spatial density of the 2DEG is affected by placement ofbody contact electrodes relative to the gate electrode, the shape of thebody contact electrodes and the gate electrode, and the applied voltagesdiscussed herein. The electric field density between the gate electrodeand the body contact electrode determines the shape of the 2DEG density.The properties or thickness of the insulator can be changed to affectthe density distribution. For example, a Bragg grating may beconstructed by patterning the gate electrode as a series of grooveshaving a constant spacing. In alternate embodiments, the gate electrodecan have a consistent thickness, but the insulator thickness or shapecan be altered to change the electrical resistance between the gateelectrode and the waveguide. All of these embodiments provide anelectrically switchable Bragg grating by controlling the 2DEG density.The 2DEG density pattern follows the surface potential at thewaveguide/electric insulator boundary rather than the exact shape of thegate electrode.

FIG. 9 shows a top view of another embodiment of optical waveguidedevice 100 that is similar to that shown in the embodiment of FIG. 2,except that the optical waveguide device includes an additional bankgate electrode 902 that is connected to a bank gate electrode well 904.The doping charge of the bank gate electrode well 904 (p++) in oneembodiment is opposite the doping charge (n++) of the source electrodewell and the drain electrode well. During operation, a voltage may beapplied between the bank gate electrode 902 and the connected sourceelectrode and drain electrode to establish a propagation constantgradient formed within the region of changeable propagation constantacross the waveguide from the source electrode to the drain electrode. Avariety of alternative embodiments may be provided to establish apropagation constant gradient formed within the region of changedpropagation constant across the waveguide. For example the width of thesecond electrical insulator layer 110, or the resistance of the materialused in the second electrical insulator layer 110 may be varied toestablish a propagation constant gradient across the waveguide. Sincethere are such a variety of FET, MOSCAP, HEMT, and other configurations,it is envisioned that those configurations are within the intended scopeof optical waveguide device of the present invention.

Optical waveguide devices may be configured either as slab waveguides orchannel waveguides. In channel waveguides, the guided light is bound intwo directions (x and y) and is free to propagate in the axialdirection. In slab waveguides, the guided light is bound in onedirection and can propagate freely in two orthogonal directions. Channelwaveguides are used in such applications as transmission, resonators,modulators, lasers, and certain filters or gratings where the guidedlight is bound in two directions. Slab waveguides are used in suchapplications as deflectors, couplers, demultiplexers, and such filtersor gratings where the guided light is bound only in one direction, andit may be desired to change the direction of propagation.

There are several embodiments of channel waveguides including the FIG.10 embodiment of the ridge channel waveguides 1000 and the FIG. 11embodiment trench channel waveguide 1100. The ridge channel waveguide1000 includes a raised central substrate portion 1002, a electricalinsulator layer 1004, and a metal gate electrode 1005. The raisedsubstrate portion 1002 is n-doped more heavily than the main substrate102. The raised substrate portion 1002 forms a channel defined by a pairof side walls 1006, 1008 on the sides; the electrical insulator layer1004 on the top, and the n-doping differential between the raisedsubstrate portion 1002 and the main substrate 102 on the bottom. Thepair of side walls 1006, 1008 includes, or is coated with, a materialhaving a similar index of refraction as the electrical insulator layers104, 106. Biasing the metal gate electrode 1005 forms a 2DEG 108adjacent the electrical insulator layer 1004. The 2DEG 108 allows thecarriers to pass between the first body contact well 107 and the secondbody contact well 109 as applied, respectively, by the respective firstbody contact electrode 118 and the second body contact electrode 122.

FIG. 11 shows one embodiment of trench channel waveguide 1100. Thetrench channel waveguide includes a plurality of electrical insulativeblocks 1102, 1104 and the waveguide 106. The electrical insulative block1102 partially extends into the waveguide 106 (from the upper surface ofthe optical waveguide device 100) at a lateral location between thefirst body contact well 107 and the gate electrode 120. The electricalinsulative block 1104 partially extends into the waveguide 106 (from theupper surface of the optical waveguide device 100) at a lateral locationbetween the second body contact well 109 and the gate electrode 120. Thelight passing through the waveguide 106 is restrained from travellinglaterally by the addition of the electrical insulative blocks 1102,1104. Spaces 1112, 1114 are defined within the waveguide between eachone of the respective insulative blocks 1102, 1104 and the firstelectrical insulator layer 104. These spaces allow carriers to flowbetween the respective first body contact well 107 and the second bodycontact well 109 through the waveguide 106 formed under the gateelectrode 120.

One embodiment of the optical waveguide devices 100 can be constructedon so-called silicon on insulator (SOI) technology that is used in thesemiconductor electronics field. SOI technology is based on theunderstanding that the vast majority of electronic transistor action inSOI transistors occurs on the top few microns of the silicon. Thesilicon below the top few microns, in principal, could be formed fromsome electrical insulator such as glass. The SOI technology is based onproviding a perfect silicon wafer formed on a layer of an electricalinsulator such as glass (silicon dioxide), that starts two to fivemicrons below the upper surface of the silicon. The electrical insulatorelectrically isolates the upper two to five microns of silicon from therest of the silicon.

The inclusion of the electrical insulator in SOI electronic deviceslimit the large number of electric paths that can be created through athicker silicon, thereby automatically making SOI transistors go fasterand use less power consumption. SOI technology has developed over thepast decade to be commercially competitive. For example, Power PC (aregistered trademark of Apple Computer, Inc. of Cupertino, Calif.) hasmoved to SOI technology. In addition, the Pentium lines of processor(Pentium is a registered trademark of Intel Corporation of Santa Clara,Calif.) is soon going to utilize the SOI technology.

The embodiment of optical waveguide device 100 shown, for example, inFIGS. 1 to 3 may be configured using SOI technology such as processorsand chips. The waveguide 106 of the optical waveguide device 100 may befashioned as the upper SOI silicon layer. The first electrical insulatorlayer 104 may be fashioned as the SOI insulator layer. The substrate 102may be fashioned as the SOI silicon substrate. As such, the SOItechnology including the majority of processors and chips, can easily beused as an optical waveguide device.

II. Waveguide Physics

This section demonstrates that the propagation constant (or equivalentlythe effective mode index) of the waveguide is an instantaneous functionof the 2DEG charge density q_(n). An increase in the free carrierdistribution in a region of the 2DEG 108 results in a correspondingincrease in the propagation constant of the waveguide 106 at thecorresponding region. The relationship between the volumetric density ofthe free carriers and the refractive index was originally derived byDrude in his Model of Metals that indicates that metals provide both adielectric and “free electron” response. The same model may be appliedto semiconductors. The changes in the real part of the refractive indexΔn and the imaginary part of the refractive index Δk (the imaginary partcorresponds to absorption) from an increase in the free carrierdistribution are a function of the change in the free-carrier densityΔN, as indicated by the following equations: $\begin{matrix}{{{\Delta\quad n} = {{\frac{e^{2}}{2ɛ_{0}m_{e}n\quad\omega^{2}}\Delta\quad N} \equiv {{\chi\Delta}\quad N}}}{{\Delta\quad k} = \frac{\Delta\quad n}{{\omega\tau}_{s}}}} & 3\end{matrix}$where e is the electronic charge, m_(e) is the effective mass of thecarrier, τ_(s) is the mean scattering time and is related to themobility, and ΔN is the change in the free-carrier density. For thesemiconductor devices considered here, where the dominant change in thefree-carriers is due to the 2DEG, ΔN is a function of q_(n) and thethickness (t) of the 2DEG varies according to the equation:$\begin{matrix}{{\Delta\quad N} = \frac{\Delta\quad q_{n}}{t_{2D\quad E\quad G}}} & 4\end{matrix}$

TABLE 1 shows the calculated values of the Drude coefficient χ and theeffective mass m_(e) for Silicon with n or p-type dopants, and GalliumArsinide (GaAs) with n-type doping (at wavelengths of 1.3 and 1.55micron). GaAs and InP both have a larger Drude Coefficient χ thansilicon. This is in part due to the smaller effective mass of charge(electron or hole). Thus, a waveguide structure made from GaAs and InPwill have larger changes in the propagation constant for the samechanges in the density of 2DEG when compared to Silicon.

TABLE 1 Wavelength Material χ m_(e) 1.33 Silicon-n   −7 × 10⁻²² 0.331.55 −9.4 × 10⁻²² 1.33 Silicon-p   −4 × 10⁻²² 0.56 1.55 −5.5 × 10⁻²²1.33 GaAs-n −3.5 × 10⁻²¹ 0.068 1.55 −4.8 × 10⁻²¹

To estimate the length requirements for a dielectric slab waveguide, themodes of the FIG. 12 embodiment of dielectric slab waveguide 106 formedbetween the cladding layers have to satisfy the equation:2k _(y) h+φ ₁+φ₂=2mπ  5

where h is the thickness of the waveguide 106, and the phase shifts φ₁and φ₂ are due to the reflection of the light at the boundary and m isan integer multiple. The propagation constant k_(z) and k_(y) arerelated to k and the mode angle θ by the following equations:$\begin{matrix}{{k_{y} = {k\quad\cos\quad\theta}}{{k_{z} = {k\quad\sin\quad\theta}},{a\quad n\quad d}}{k = {\left( \frac{2\pi}{\lambda} \right)n}}} & 6\end{matrix}$

Solving equations 5 and 6 can derive the modes of the waveguide 106. Thevalues of φ₁ and φ₂ are functions of angle θ. The change in thepropagation constant k_(z) due to change in the waveguide index profileinduced by the 2DEG is responsible for amplitude and phase modulation.The phase modulation of the light in the waveguide results from a changein the propagation constant of selected regions within the waveguide.The amplitude modulation of the light passing through the waveguideresults from a change in the absorption of the light passing throughselected regions within the waveguide.

The shape and type of the material through which light is passing playsan important role in determining the optical function of the opticalwaveguide device. For example, light passing through rectangular slaboptical waveguide device only travels axially along the optical path101. Optical deflectors, for example, not only allow the light to travelaxially, but can also deviate the light laterally. The amount ofdisplacement and deviation of the light passing through the waveguideare both dependent on the propagation constant of the waveguide as wellas the apex angle of the prism.

The shape of a region of changeable propagation constant 190 within awaveguide plays a role in determining how an application of voltage tothe gate electrode will modify the optical characteristics of lightpassing through the waveguide. For example, a suitably-biasedprism-shaped gate electrode projects a three dimensional prism-shapedregion of changeable propagation constant 190 into the waveguide. Thecross-sectional height of the region of changeable propagation constant190 is projected through the entire height of the waveguide. As viewedfrom above, the region of changeable propagation constant 190 deflectslight in similar propagation directions as light passing through asimilarly shaped optical prism. In slab waveguides, the rays of lightwill deflect or bounce between the upper and lower surface of thewaveguide while continuing in the same propagation direction as viewedfrom above.

Unlike actual optical devices that are physically inserted in a path oflight, any effects on light passing through the waveguide of the presentinvention due to the propagation constant within a region of changeablepropagation constant 190 can be adjusted or eliminated by altering thevoltage level applied to the gate electrode. For example, reducing thevoltage applied to a deflector-shaped gate electrode sufficientlyresults in the propagation constant of the projected deflector-shapedregion of changeable propagation constant 190 being reduced to thepropagation constant value of the volume surrounding the region ofchangeable propagation constant 190. In effect, the region of changeablepropagation constant 190 will be removed. Light travelling through theregion of changeable propagation constant 190 will therefore not beeffected by the region of changeable propagation constant 190 within thewaveguide. Similarly, the strength of the propagation constant can bechanged or reversed by varying the voltage applied to the gateelectrode.

III. Specific Embodiments of Optical Waveguide Devices

A variety of embodiments of optical waveguide devices are now described.Each optical waveguide device shares the basic structure and operationof the embodiments of optical waveguide device described relative toFIGS. 1-3, 4, or 5. The optical waveguide device can be configured ineither the channel waveguide or slab waveguide configuration. Eachembodiment of optical waveguide device is an active device, andtherefore, the voltage level applied to the electrode can control thedegree that the light within the region of changeable propagationconstant 190 in the waveguide will be affected. Since the opticalwaveguide device is active, the propagation constant in the region ofchangeable propagation constant 190 can be adjusted by varying thevoltage applied to the gate electrode. Allowing for such adjustmentusing the controller 201 in combination with either the meter 205 or thetemperature sensor 240 using the methods shown in FIGS. 7 or 8 is highlydesirable considering the variation effects that temperature, deviceage, pressure, etc. have on the optical characteristics of the opticalwaveguide device.

The embodiments of optical waveguide device 100 described relative toFIGS. 1 to 3, 4, and 5 can be modified to provide a considerablevariation in its operation. For example, the optical waveguide device100 can have a projected region of changeable propagation constant 190within the waveguide to provide one or more of phase and/or amplitudemodulation, optical deflection, optical filtering, optical attenuation,optical focusing, optical path length adjustment, variable phase tuning,variable diffraction efficiency, optical coupling, etc. As such,embodiments of many optical waveguide devices that perform differentoperations are described in the following sections along with theoperations that they perform.

In each of the following embodiments of an optical waveguide device, thegate electrode is formed in a prescribed electrode shape to perform adesired optical operation. The projected region of changeablepropagation constant 190 assumes a shape similar to, but not necessarilyidentical to, the gate electrode. The shape of the region of changeablepropagation constant 190 within the waveguide can physically mapextremely closely to, with a resolution of down to 10 nm, the prescribedgate electrode shape. The construction and operation of differentembodiments of optical waveguide devices, and the operation, and effectsof various embodiments of regions of changeable propagation constant 190are described in this section.

3A. Optical Modulator

This section describes an optical modulator, one embodiment of opticalwaveguide device 100 that modulates light passing through the waveguide.The embodiments of optical waveguide device as shown in FIGS. 1-3, 4, or5 can perform either phase modulation or amplitude modulation of lightpassing through the waveguide. The modulation of light by the opticalwaveguide device 100 can be optimized by reducing the losses in the gateelectrode 120 as well as reducing the charges in the 2DEG 108, whileincreasing the interaction of the waveguide mode with the 2DEG. Ingeneral, reducing the waveguide thickness h reduces the necessarywaveguide length L_(N) to produce modulation. Limiting the modulation ofthe 2DEG 108 also limits the effects on the free-carriers resulting fromabsorption during modulation. The length required for a specific loss,such as a 10 dB loss L_(10dB), can be experimentally determined for eachdevice. Both L_(N) and L₁₀dB are functions of Δq_(n). Δq_(n) depends onboth the DC bias V_(g) as well peak-to-peak variation of the varying ACsignal v_(g).

To construct a high-speed modulator operating with bandwidth in excessof, for example 50 GHz, it is important to consider both the RFmicrowave interfaces and the transit time of the free-carriers. Sincethe carriers arrive in the 2DEG either from the bulk electrode (notshown), from the first body contact electrode 118, or from the secondbody contact electrode 122, as the voltage of the gate electrode 122 ischanged, the time required for the voltage to equilibrate to supply aconstant voltage is, $\begin{matrix}{\tau_{e} = \frac{\left( {L/2} \right)}{v_{s}}} & 7\end{matrix}$where v_(s) is the maximum velocity of the carriers and L is the channellength illustrated in FIG. 1. Thus, the maximum length L of the MOS/HEMTstructure of the optical waveguide device 100 is determined by therequirement that τ_(e) be less than some percentage of the bit period.

FIG. 6 shows illustrative graph of the surface charge density and thephase shift, both plotted as a function of the surface potential for aplanar dielectric waveguide. In the FIG. 6 plot, the waveguide is anexemplary planar Si waveguide that has an electrical insulator layersuch as cladding on both the upper and lower surfaces. The waveguide isa single mode waveguide with the propagation constant of 14.300964 μm⁻¹.A change in the gate voltage by approximately 0.2-0.5 V results in achange to the surface charge density of the 2DEG by 8×10¹² cm⁻² which inturn will lead to a change of −0.01 in the propagation constant if the2DEG was due to electrons. Further assume that this 2DEG region iseffectively confined to within 5-50 nm adjacent the upper electricalinsulator layer, as is typical for MOS device physics. Assuming thatthere is an index change over only a 10 nm distance, the new propagationconstant is calculated to be 14.299792 μm⁻¹. The changes in thepropagation constant result in an additional phase shift of 180 degreesfor light travelling a length of 2.86 mm. Thus, gate voltage modulationleads to phase modulation of light in the waveguide. Similarly,free-carrier absorption occurs in the semiconductor locations wherethere are scattering centers (i.e. donor sites). Such free-carrierabsorption acts to modulate the amplitude of the propagating mode oflight. In general, amplitude modulation and phase shift modulation willoccur simultaneously, but one type of modulation can be arranged to bepredominant by controlling the doping profile of the waveguide.

In one embodiment, a channel waveguide is used to construct a high-speedmodulator. With total internal reflection (TIR) using a channelwaveguide, all the light within the waveguide is constrained to followthe direction parallel to the optical path 101 since the light thatcontacts the electrical insulator layers 104, 110 of the waveguidereflects off the electrical insulator layers. Electrical insulatorlayers 104, 110 have a lower refractive index than the waveguide. Thechannel waveguide should be dimensioned to match the mode(s) of thewaveguide so the waveguide acts as a modulator for that mode.

The first body contact well 107 and the second body contact well 109,that respectively interact with the first body contact electrode 118 andthe second body contact electrode 122, are both typically n-doped. Thisdoping produces the body contact wells 107, 109 having a lowerrefractive index than the silicon waveguide 106 due to the presence offree-carriers. The body contact wells 107, 109 thus form alow-refractive index cladding that naturally confine the light mode(s)laterally within the waveguide 106. The body contact wells 107, 109 alsoabsorb some light passing through the waveguide 106, but the absorptionof light makes the waveguide lossy. Thus, it may be desired to use otherrefractive elements than the electrodes 118, 122 to confine the travelof the optical modes and limit the loss of the light.

For high speed modulation, the body contacts and the gate electrodes canbe made to act like a waveguide that operates at radio frequencies. Itis preferred, depending on the distance required, to produce therequired modulation to match the group velocity of the optical wave tothe microwave.

Variable optical attenuators are one additional embodiment of opticalamplitude modulators. The description of constructing one embodiment ofvariable optical attenuator using optical waveguide devices is describedlater following a description of Bragg gratings.

3B. Optical Deflectors

The FIG. 13 embodiment of the optical waveguide device 100 is capable ofacting as an optical deflector 1300 to controllably deflect lightpassing through the waveguide. In one embodiment of deflector 1300, thegate electrode 120 shown in the embodiments of FIGS. 1-3, 4, and 5 isphysically and operationally divided into two electrodes including theinput prism gate electrode 1304 and the output prism gate electrode1306. Both the input prism gate electrode 1304 and the output prism gateelectrode 1306 may be shaped in a trapezoidal or other prismatic)configuration, and are both substantially co-planar and physicallypositioned above the waveguide. When voltage of a first polarity isapplied to one of the input prism gate electrode 1304 or the outputprism gate electrode 1306 (not simultaneously), light will be deflectedfrom the incident axial direction of propagation into opposite lateraldirections, e.g. respectively downwardly and upwardly within thewaveguide of FIG. 13. When a voltage of one polarity is applied to oneof the input prism gate electrode 1304, light will be deflected in theopposite lateral directions (upward or downward as shown in FIG. 13) aswhen voltage of the same polarity is applied to the output prism gateelectrode 1306.

The input prism gate electrode 1304 and the output prism gate electrode1306 are both formed from an electrically conductive material such asmetal. A first voltage supply 1320 extends between the combined firstbody contact electrode 118 and second body contact electrode 122 (thatare electrically connected by substantially constant potential conductor204) and the input prism gate electrode 1304. A second voltage supply1322 extends between the combined first body contact electrode 118 andsecond body contact electrode 122 to the output prism gate electrode1306. The first voltage supply 1320 and the second voltage supply 1322are individually controlled by the controller 201, and therefore anopposite, or the same, or only one, or neither, polarity voltage can beapplied to the input prism gate electrode 1304 and the output prism gateelectrode 1306. The input prism gate electrode 1304 and the output prismgate electrode 1306 can be individually actuated so that each one of thedeflecting prism gate electrodes 1304, 1306 can project a region ofchangeable propagation constant 190 in the waveguide while the otherdeflecting prism gate electrode does not. FIGS. 14 and 15 show a shapeof a embodiment of first region of changeable propagation constant 190 aprojected by the input prism gate electrode 1304 closely maps that shapeof the input prism gate electrode shown in FIG. 13. The shape of theFIGS. 14 and 15 embodiment of second region of changeable propagationconstant 190 b projected by the output prism gate electrode 1306 thatclosely maps that shape of the output prism gate electrode 1306 shown inFIG. 13.

The input prism gate electrode 1304 has an angled surface 1308 whosecontour is defined by apex angle 1312. The output prism gate electrode1306 has an angled surface 1310 whose contour is defined by apex angle1314. Increasing the voltage applied to either the input prism gateelectrode 1304 or the output prism gate electrode 1306 increases thefree carrier distribution in the region of the 2DEG adjacent therespective first region of changeable level of region of changeablepropagation constant 190 a or the second region of changeablepropagation constant 190 b of the waveguide, shown in the embodiment ofFIG. 15 (that includes FIG. 15A to 15D). Both regions of changeablepropagation constants 190 a, 190 b are prism (trapezoid) shaped andextend for the entire height of the waveguide and can be viewed as ahorizontally oriented planar prisms located in the waveguide whose shapein the plane parallel to the gate electrode is projected by therespective deflecting prism gate electrodes 1304, 1306. The waveguidevolume within either one of the regions of changeable propagationconstant 190 a, 190 b has a raised propagation constant compared tothose waveguide regions outside the region of changeable propagationconstant 190 a, 190 b. Additionally, a boundary is formed between eachone of the regions of changeable propagation constant 190 a, 190 b andthe remainder of the waveguide. The fact that each one of the regions ofchangeable propagation constant 190 a, 190 b has both a raisedpropagation constant level and a boundary makes the prism-shaped regionsof changeable propagation constant 190 a, 190 b act as, and indeed befunctionally equivalent to, optical prisms formed of eithersemiconductor material or glass.

As shown in FIG. 15A, when a level of voltage that is insufficient toalter the carrier concentration is applied to either gate electrode 1304and 1306, no 2DEG 108 is established between the electric insulatorlayer 110 and the waveguide 106. Since the 2DEG changes the level ofpropagation constant in the respective regions of propagation constant190 a, 190 b, no regions of changeable propagation constants 190 a or190 b are established in the waveguide 106. Therefore, the propagationconstant of the first region of changeable propagation constant 190 a inthe waveguide matches the propagation constant level of the remainder ofthe waveguide 106, and light travelling along paths 1420, 1422 continuesto follow their incident direction. Path 1420 is shown with a wavefront1440 while path 1422 is shown with a wavefront 1442.

When voltage of a first polarity is applied to the input prism gateelectrode 1304, the first region of changeable propagation constant 190a is projected in the shape of the input prism gate electrode 1304through the height of the waveguide to form the region of changedpropagation constant 190 a, as shown in FIG. 15B. The first region ofchangeable propagation constant 190 a thus functions as a variableoptical prism that can be selectively turned on and off. The firstregion of changeable propagation constant 190 is formed in thesemiconductor waveguide that deflects the light passing along thewaveguide along a path 1430 including wavefronts 1432. Individual beamsof the light following path 1430 are reflected with total internalreflectance between an upper and lower surface of the waveguide, but thedirection of travel of light within the waveguides remains along thepath 1430.

The intensity of the voltage applied to the input prism gate electrode1304 can be reduced to limit the propagation constant level of theregion of changed propagation constant, so the light following path 1420would be deflected, e.g., along path 1436 instead of along path 1430.The polarity of the voltage applied to the input prism gate electrode1304 can also be reversed, and light following path 1420 along thewaveguide would be deflected to follow path 1438. Therefore, thedeflection of the light within the waveguide 106 can be controlled, andeven reversed, by controlling the voltage applied to the input prismgate electrode 1304. Changing of the propagation constant within thefirst region of changeable propagation constant 190 a causes suchdeflection by the input prism gate electrode 1304.

When no voltage is applied to the output prism gate electrode 1306 asshown in FIGS. 15A and 15B, thereby effectively removing the secondregion of changeable propagation constant 190 b from the waveguide 106.Light following within waveguide 106 along path 1422 is assumed tocontinue in a direction aligned with the incident light, or in adirection deflected by the input prism gate electrode 1304, since thepropagation constant is uniform throughout the waveguide.

When voltage of a first polarity is applied to the output prism gateelectrode 1306, the second region of changeable propagation constant 190b having a changed propagation constant level is projected in thewaveguide as shown in FIGS. 15C and 15D. The second region of changeablepropagation constant 190 b may be viewed as an optical prism thatprojects in the shape of output prism gate electrode 1306 to thewaveguide, thereby deflecting the light passing along the waveguidealong path 1460 with the wavefronts 1462 extending perpendicular to thedirection of travel.

The intensity of the voltage applied to the output prism gate electrode1306 shown in FIG. 15C can be reduced, so the light following path 1422would be deflected at a lesser angle, e.g., along path 1466 instead ofalong path 1460. Similarly, increasing the voltage applied to the outputprism gate electrode 1306 increases the angle of deflection. Thepolarity of the voltage applied to the output prism gate electrode 1306could also be reversed, and light following path 1420 within thewaveguide would be deflected in a reversed direction to the originalpolarity to follow path 1468. Therefore, the deflection of the lightwithin the waveguide 106 can be controlled, and even reversed, bycontrolling the voltage applied to the output prism gate electrode 1306.Additionally, the propagation constant in prescribed regions of thewaveguide, and the gate resistance, can be calibrated using thetechniques described in FIGS. 7 and 8 using the controller 201, themeter 205, and/or the temperature sensor 240.

The voltage being used to bias the input prism gate electrode 1304and/or the output prism gate electrode 1306 have the effect ofcontrollably deflecting the light as desired. The FIG. 14 embodiment ofoptical waveguide device 100 is structurally very similar to the FIGS. 1to 3 embodiment of optical waveguide device 100, however, the twoembodiments of optical waveguide devices perform the differing functionsof modulation and deflection.

In the FIG. 16 embodiment of optical waveguide device, the incidentlight flowing through the waveguide will be deflected from its incidentdirection in a direction that is parallel to the axis of the opticalwaveguide device. Such deflection occurs as result of variable voltageapplied between the second body contact electrode 122 and the first bodycontact electrode 118. In this configuration, an additional voltagesource 1670 applies a voltage between the second body contact electrodeand the first body contact electrode to provide voltage gradient acrossthe gate electrode. By varying the voltage between the second bodycontact electrode and the first body contact electrode, the level ofpropagation constant within the region of changeable propagationconstant changes. The voltage level applied to the waveguide thus causesa direction of the propagation of light flowing through the waveguide tobe controllably changes, leading to deflection of light within thehorizontal plane (e.g. upward and downward along respective paths 1672,1674 as shown in FIG. 16).

The application of the first body contact-to-second body contact voltageV_(SD) 1670 by the voltage source causes a propagation constant gradientto be established across the 2DEG in the waveguide 106 from the firstbody contact electrode to the second body contact electrode. Thus, thepropagation constant, or the effective mode index, of the waveguide 106,varies. This variation in the propagation constant leads to angled phasefronts from one lateral side of the waveguide to another. That is, thewavefront of the optical light flowing through the FIG. 16 embodiment ofwaveguide 106 on one lateral side of the wavefront lags the wavefront onthe other lateral side. The phase fronts of the light emerging from thegate region will thus be tilted and the emerging beam will be deflectedby an angle γ. For a fixed V_(DS), the deflection angle γ increases withthe distance z traveled within the waveguide 106. The angle γ can becalculated by referring to FIG. 16 according to the equation.$\begin{matrix}{\gamma = {{a\quad{\tan\left( \frac{\Delta\quad O\quad P}{L} \right)}} = {{a\quad{\tan\left( \frac{\Delta\quad\overset{\_}{n}\quad W}{L} \right)}} = {{{a\quad{\tan\left( \frac{\overset{\_}{n}\quad{\cot(\theta)}{\Delta\theta}\quad W}{L} \right)}}\therefore\gamma} = {\left( \frac{W}{L} \right)10^{- 4}}}}}} & 8\end{matrix}$

Another embodiment of optical deflector 1700 is shown in FIG. 17. Thewaveguide 1702 is trapezoidal in shape. A gate electrode 1706 (that isshown as hatched to indicate that the gate electrode shares the shape ofthe waveguide 1702 in this embodiment) may, or may not, approximate thetrapezoidal shape of the waveguide. Providing a trapezoidal shapedwaveguide in addition to the shaped gate electrode enhances thedeflection characteristics of the optical deflector on light. In theoptical deflector 1700, if the voltage applied to the gate electrode isremoved, deflection occurs due to the shape of the waveguide due to thetrapezoidal shape of the waveguide. In this embodiment of opticalwaveguide device, the waveguide itself may be shaped similarly to theprior-art discrete optical prisms formed from glass.

FIG. 18 shows one embodiment of optical switch 1800 including aplurality of optical deflectors that each switches its input light fromone or more deflecting prism gate electrodes 1802 a through 1802 e toone of a plurality of receiver waveguides 1808 a to 1808 e. The opticalswitch 1800 includes an input switch portion 1802 and an output switchportion 1804. The input switch portion includes a plurality of the FIG.18 embodiment of deflecting prism gate electrodes as 1802 a to 1802 e.The deflecting prism gate electrodes 1802 a to 1802 e may each beconstructed, and operate, as described relative to one of the deflectingprism gate electrodes 1306, 1308 of FIG. 13. Each one of the deflectingprism gate electrodes 1802 a to 1802 e is optically connected at itsinput to receive light signals from a separate channel waveguide, notshown in FIG. 18. The output portion 1806 includes a plurality ofreceiver waveguides 1808 a, 1808 b, 1808 c, 1808 d, and 1808 e. Each ofthe receiver waveguides 1808 a to 1808 e is configured to receive lightthat is transmitted by each of the deflecting prism gate electrodes 1802a to 1802 e.

The optical switch 1800 therefore includes five deflecting prism gateelectrodes 1802 a to 1802 e, in addition to five receiver waveguides1808 a to 1808 e. As such, the optical switch can operate as, e.g., a5×5 switch in which any of the deflecting prism gate electrodes 1802 ato 1802 e can deflect it's output light signal to any, or none, of thereceiver waveguides 1808 a to 1808 e. Each of the deflecting prism gateelectrodes 1802 a to 1802 e includes a gate portion that is configuredwith a respective angled apex surface 1810 a to 1810 e. Voltage suppliedto any of the deflecting prism gate electrodes 1802 a to 1802 e resultsin an increase in the propagation constant within the correspondingregion of changeable propagation constant 190 (that forms in thewaveguide below the corresponding deflecting prism gate electrode 1802 ato 1802 e shown in FIG. 18) associated with that particular deflectingprism's gate electrode.

Although the FIG. 18 embodiment of waveguide operates similarly to theFIG. 15 embodiment of waveguide, if no voltage is applied to anyparticular deflecting prism gate electrode 1802 a to 1802 e, then thelight travels directly through the waveguide associated with thatdeflecting prism gate electrode and substantially straight to arespective receiver waveguide 1808 a to 1808 e located in front of thatdeflecting prism gate electrode. The apex angles 1810 a and 1810 e(and/or the angles of the waveguide as shown in the FIG. 17 embodiment)of the outer most deflecting prism gate electrodes 1802 a and 1802 e areangled at a greater angle than deflecting prism gate electrodes 1802 b,1802 c, and 1802 d. An increase in the apex angle 1810 a and 1810 eallows light flowing through the waveguide to be deflected through agreater angle toward the more distant receivers 1808 a to 1808 e. It mayalso be desired to minimize the lateral spacing between each successivedeflecting prism gate electrode 1802 a to 1802 e, and the lateralspacing between each respective receiver 1808 a to 1808 e to minimizethe necessary deflection angle for the deflecting prism gate electrodes.The apex angle of those deflecting prism gate electrodes that aregenerally to the left of an axial centerline of the optical switch (andthus have to deflect their light to the right in most distances) areangled oppositely to the apex angle of those deflecting prism gateelectrodes that are to the right of the centerline of that switch thathave to deflect their light to the left in most instances. Deflectingprism gate electrodes 1802 b, 1802 c, and 1802 d that have otherdeflecting prism gate electrodes locate to both their right and leftshould also have receivers located both to their right and left as shownin FIG. 18 and therefore must be adapted to provide for deflection oflight to either the left or right. For example, the deflecting prismgate electrode 1802 c must cause light traveling through its waveguideto be deflected to the right when transmitting its signal to thereceivers 1808 d or 1808 e. By comparison, the deflecting prism gateelectrode 1802 c must cause light that is passing through its waveguideto be deflected to its left when deflecting light to receivers 1808 aand 1808 b.

Optical switch 1800 has the ability to act extremely quickly, partly dueto the fact that each deflecting prism gate electrode has no movingparts. Each of the deflecting prism gate electrodes 1802 a to 1802 e canbe adjusted and/or calibrated by controlling the voltage applied to thatdeflecting prism gate electrode using the techniques described in FIGS.7 and 8. Applying the voltage to the deflecting prism gate electrodes1802 a to 1802 e results in an increase, or decrease (depending onpolarity), of the propagation constant level of the region of changeablepropagation constant in the waveguide associated with that deflectingprism gate electrode 1802 a to 1802 e.

FIG. 19 shows another embodiment of optical switch 1900. The opticalswitch includes a concave input switch portion 1902 and a concave outputswitch portion 1904. The input switch portion 1902 includes a pluralityof deflecting prism gate electrodes 1902 a to 1902 d (having respectiveapex angles 1910 a to 1910 d) that operate similarly to the FIG. 18embodiment of deflecting prism gate electrodes 1802 a to 1802 e.Similarly, the concave output switch portion 1902 includes a pluralityof receivers 1908 a to 1908 d. Each one of the receivers 1908 a to 1908d operates similarly to the FIG. 18 embodiment of receivers 1808 a to1808 e. The purpose of the concavity of the concave input switchdeflector portion 1902 and the concave output portion 1904 is tominimize the maximum angle through which any one of the opticaldeflecting prism gate electrodes has to deflect light to reach any oneof the receivers. This is accomplished by mounting each of the opticaldeflecting prism gate electrodes at an angle that bisects the raysextending to the outermost receivers 1908 a to 1908 d. The mounting ofthe optical deflecting gate electrodes also generally enhances thereception of light by the receivers since each receiver is directed atan angle that more closely faces the respective outermost opticaldeflecting prism gate electrodes. The operation of the embodiment ofoptical switch 1900 in FIG. 19 relative to the deflecting prism gateelectrodes 1902 a to 1902 d and the receivers 1908 a and 1908 d issimilar to the above-described operation of the optical switch 1800 inFIG. 18 relative to the respective deflecting prism gate electrodes 1802a to 1808 e (except for the angle of deflection of the deflecting prismgate electrode).

3C. Optical Gratings

Bragg Gratings in the dielectric slab waveguide as well as in fibers arewell known to perform various optical functions such as opticalfiltering, group velocity dispersion control, attenuation, etc. Thefundamental principle behind Bragg grating is that small, periodicvariation in the mode index or the propagation constant leads toresonant condition for diffraction of certain wavelengths.

These wavelengths satisfy the resonant condition for build up ofdiffracted power along certain direction. The wavelength selectivitydepends on the design of the grating structure. In the case presentedhere, we envision a Bragg grating that is electrically controlled viathe effect of 2DEG. There are many ways to produce the undulatingpattern in 2DEG. The methods include: undulation in the effectivedielectric constant of the gate insulator, patterned gate metal,periodic doping modulation etc. FIG. 20 is one example. In FIG. 20 thegate dielectric is divided into two gate insulators of differentdielectric strength.

FIGS. 20 to 22 show a variety of embodiments of optical Bragg gratingsin which the shape or configuration of the gate electrode 120 of theoptical waveguide device 106 is slightly modified. Bragg gratingsperform a variety of functions in optical systems involving controllableoptical refraction as described below. In the different embodiments ofoptical Bragg gratings, a series of planes of controllable propagationconstant (compared to the surrounding volume within the waveguide) areprojected into the waveguide 106. The planes of controllable propagationconstant may be considered to form one embodiment of a region ofchangeable propagation constant 190, similar to those shown anddescribed relative to FIGS. 1-3, 4, or 5. In the FIG. 20 embodiment ofoptical Bragg grating 2000, the second insulator layer 110 is providedwith a corrugated lower surface 2002. The corrugated lower surfaceincludes a plurality of raised lands 2004 that provide a variablethickness of the second insulator layer 110 between different portionsof the corrugated lower surface of the second electrical insulator layeror oxide 110 and the gate electrode 120. Each pair of adjacent raisedlands 2004 are uniformly spaced for one Bragg grating.

A distance T1 represents the distance between the raised lands 2004 ofthe corrugated surface 2002 and the gate electrode 120. A distance T2represents the distance from the lower most surface of the corrugatedsurface 2002 and the gate electrode 122. Since the distance T1 does notequal T2, the electrical field at the insulator/semiconductor interfaceof the second insulator layer 110 from the gate electrode to thewaveguide 106 will vary along the length of the waveguide. For example,a point 2006 in the waveguide that is underneath the location of one ofthe raised lands 2004 experiences less electrical field at theinsulator/semiconductor interface to voltage applied between the gateelectrode and the waveguide than point 2008 that is not underneath thelocation of one of the raised lands. Since the resistance of the secondinsulator layer 110 in the vertical direction varies along its length,the resistance between the gate electrode and the waveguide (that hasthe second insulating layer interspersed there between) varies along itslength. The strength of the electric field applied from the gateelectrode into the waveguide varies as a function of the thickness ofthe second insulator layer 110. For example, the projected electricfield within the waveguide at point 2006 exceeds the projected electricfield at point 2008. As such, the resultant free carrier chargedistribution in the 2DEG above point 2006 exceeds the resultant freecarrier charge distribution in the 2DEG above point 2008. Therefore, theresultant propagation constant in the projected region of changeablepropagation constant 190 in the waveguide at point 2006 exceeds theresultant propagation constant in the projected region of changeablepropagation constant 190 in the waveguide at point 2008.

The raised lands 2004 are typically formed as grooves in the secondinsulator layer 110 that extend substantially perpendicular to, orangled relative to, the direction of light propagation within thewaveguide. The raised lands 2004 may extend at a slight angle asdescribed with respect to FIG. 23 so that reflected light passingthrough the waveguide may be deflected at an angle to, e.g., anotherdevice. A low insulative material 200 is disposed between the secondelectrical insulator layer 110 and waveguide 106. The previouslydescribed embodiments of optical waveguide devices relied on changes inthe planar shape of the gate electrode to produce a variable region ofchangeable propagation constant 190 across the waveguide. The FIGS. 20to 22 embodiments of optical waveguide devices rely on variations ofthickness (or variation of the electrical resistivity of the material)of the gate electrode, or the use of an insulator under the gateelectrode, to produce a variable propagation constant across thewaveguide.

Since a variable electromagnetic field is applied from the gateelectrode 120 through the second electrical insulator layer or oxide 110to the waveguide 106, the propagation constant of the waveguide 106 willvary. The carrier density in the 2DEG 108 will vary between the locationin the 2DEG above the point 2006 and above the point 2008. Moreparticularly, the lower resistance of the second electrical insulatorlayer or oxide at point 2006 that corresponds to distance T1 will resultin an increased carrier density compared to the point 2008 on the 2DEGthat corresponds to an enhanced distant T2, and resulting in anincreased resistance of the 2DEG. Such variation in the propagationconstant along the length of the waveguide 106 results only when gateelectrode 120 is actuated. When the gate electrode is deactuated, thepropagation constant across the waveguide 106 is substantially uniform.In the FIGS. 20 to 22 embodiments of optical gratings, the propagationconstant is changed by the thickness of the gate electrode, i.e., theraised lands locations. Therefore, this embodiment of optical waveguidedevice changes the propagation constant by changing the thickness of thegate electrode to form the Bragg gratings, not by changing the shape ofthe gate electrode.

Such a variation in propagation constant within certain regions at thewaveguide 106 will result in some percentage of the light travelingalong the waveguide 106 to be reflected. The variation in thepropagation constant extends substantially continuously across thelength of the FIG. 20 embodiment of waveguide 106. As such, even thougha relatively small amount of energy of each light wave following adirection of light travel 101 will be reflected by each plane projectedby a single recess, a variable amount of light can be controllablyreflected by the total number of planes 2012 in each Bragg grating. Thedistance d in the direction of propagation of light between successiveplanes within the Bragg grating is selected so that the lightwavesreflected from planes 2012 are in phase, or coherent, with the lightreflected from the adjacent planes. The strength of the 2DEG determinesthe reflectivity or the diffraction efficiency of the Bragg structure.By varying the strength, we may chose to control the light diffracted bythe Bragg structure. This will be useful in construction of theattenuators, modulators, switches etc.

The lightwaves travelling in direction 101 from the adjacent phaseplanes 2012 will be in phase, or coherent, for a desired light ofwavelength λ if the difference in distance between light reflected fromsuccessive planes 2012 equals an integer multiple of the wavelength ofthe selected light. For example, light traveling along the waveguide 106(in a direction from left to right as indicated by the arrow inwaveguide 106) that is reflected at the first plane 2012 (the planefarthest to the left in FIG. 20) is reflected either along the waveguide106 or at some angle at which the reflected light beam is deflected, andtravels some distance shorter than light reflected off the next plane(the first plane to the right of the leftmost plane 2012 in FIG. 20).

Light reflected from the Bragg gratings of the waveguide will bein-phase, or coherent, when the distance d between recesses taken in adirection parallel to the original direction of propagation of the lightin the waveguide is an integer multiple of a selected bandwidth oflight. In the FIG. 23 embodiment of Bragg grating, light reflected offsuccessive planes 2311 would coherently add where the distance “d” issome integer multiple of the wavelength of the reflected light. Theother wavelengths of light interfere destructively, and cannot bedetected by a detector.

The FIG. 21 embodiment of Bragg grating 2100 includes a plurality ofinsulators 2102 evenly spaced between the electrical insulator layer 110and the waveguide 106. The electrical resistance of the insulators 2102differs from that of the electrical insulator layer 110. Alternatively,inserts could be inserted having a different electrical resistance thanthe remainder of the electrical insulator layer. The insulator 2102limits the number of carriers that are generated in those portions ofthe 2DEG 108 below the insulators 2102 compared to those locations inthe 2DEG that are not below the insulators 2102. As such, thepropagation constant in those portions of the waveguide 106 that arebelow the insulators 2102 will be different than the propagationconstant in those portions of the waveguide that are not below theinsulators 2102. Planes 2112 that correspond to the regions of changedpropagation constant within the waveguide under the insulators that areprojected into the waveguide 106. Such planes 2112 are thereforeregularly spaced since the location of the projected regions ofchangeable propagation constant corresponds directly to the location ofthe insulators 2102. The insulator properties that control the strengthof the electric field at the insulator/semiconductor interface are dueto its dielectric constant at the modulation frequencies of interest.The insulator may have variable dielectric constant at radio frequenciesbut is substantially unchanged at the optical frequencies. Thus, opticalwave does not “see” the undulation unless induced by 2DEG.

In the FIG. 22 embodiment of optical Bragg grating 2200, another shapeof regularly shaped patterning, that may take the form of corrugatedpatterns along the bottom surface of the gate electrode 120, is formedin the gate electrode 120. The optical Bragg grating 2200 includes aseries of raised lands 2202 formed in the lower surface the of the metalgate electrode 120. These raised lands 2202 may be angled relative tothe waveguide for a desired distance. The raised lands 2202 in the gateelectrode are configured to vary the electrical field at theinsulator/semiconductor interface to the waveguide 106 in a patterncorresponding to the arrangement of the raised lands 2202. For example,the propagation constant will be slightly less in those regions of thewaveguide underneath the raised lands 2202 than in adjacent regions ofthe waveguide since the distance that the raised lands 2202 areseparated from the waveguide is greater than the surrounding regions.

In this disclosure, Bragg gratings may also be configured using a SAW,or any other similar acoustic or other structure that is configured toproject a series of parallel planes 2112 representing regions ofchangeable propagation constant into the waveguide 106.

The planes 2311 are each angled at an angle α from the direction ofpropagation of the incident light 2304. As such, a certain amount oflight is reflected at each of the planes 2311, resulting in reflectedlight 2306. The majority of light 2304 continues straight through thewaveguide past each plane 2311, with only a relatively minor portionbeing reflected off each plane to form the reflected light 2306. Thedifference in distance traveled by each successive plane 2311 thatreflects light is indicated, in FIG. 23, by the distance d measured in adirection parallel to the incident light beam 2304. Therefore, distanced is selected to be some multiple of the wavelength of the light that isto be reflected from the FIG. 23 embodiment of optical Bragg grating.The selected wavelength λ of light that reflect off successive planesspaced by the distance d must satisfy the equation:2 sin α=λ/d  9

If each reflected light path 2306 distance varies by an integer multipleof the wavelength of the selected light, the light at that selectedwavelength will constructively interfere at a detector 2312 and thus bevisible. The detector can be any known type of photodetector. Since thedistance d has been selected at a prescribed value, the distance of eachray of reflected light 2306 off each plane travels a slightly greaterdistance than a corresponding ray of light reflected off the precedingplane (the preceding plane is the plane to the left as shown in FIG.23). Those wavelengths of light that are not integer multiples of thedistance d, will interfere destructively and thus not be able to besensed by the detector 2312.

The Bragg gratings represent one embodiment of a one-dimensionalperiodic structure. More complicated optical functions may be achievedby using a two dimensional periodic patterns. One embodiment of atwo-dimensional periodic structure that corresponds to the Bragg gratingincludes using a “polka dot” pattern, in which the reflectivity of aparticular group of wavelengths are unity in all directions in theplane. A “line defect” in the pattern may be provided that results inthe effective removal of one or more of these “polka dots” along a linein a manner that causes guiding of light along the line defect. Manygeometrical shapes can be used in addition to circles that form thepolka dot patter. All of these can be achieved by generalization of theBragg gratings discussed in detail above to the one-dimensionalpatterns.

FIG. 23 shows one embodiment of optical Bragg grating 2303 that isconfigured to diffract light. A series of such optical Bragg gratingslabeled as 2303 a to 2303 e can be applied to the FIG. 24 embodiment ofwaveguide. The specific optical Bragg grating 2303 relating to a desiredwavelength λ of light can be actuated, while the remainder of theoptical Bragg gratings 2303 are deactuated. One design may provide aplurality of optical Bragg gratings 2303 arranged serially along achannel waveguide, with only a minimal difference between thewavelengths λ of the reflected light by successive optical Bragggratings 2303 a to 2303 e. For example, the first optical Bragg grating2303 a reflects light having a wavelength λ₁ that exceeds the wavelengthλ₂ of the light that is diffracted by the second optical grating 2303 b.Similarly, the wavelength of light that can be reflected by each opticalBragg grating is greater than the wavelength that can be reflected bysubsequent Bragg gratings. To compensate for physical variations in thewaveguide (resulting from variations in temperature, device age,humidity, or vibrations, etc.), a Bragg grating that corresponds to adesired wavelength of reflected light may be actuated, and then thereflected light monitored as per wavelength. If multiple optical Bragggratings are provided to allow for adjustment or calibration purposes,then the differences in spacing between successive planes of thedifferent optical Bragg gratings is initially selected. If it is foundthat the actuated Bragg grating does not deflect the desired light (thewavelength of the deflected light being too large or too small), thenanother optical Bragg grating (with the next smaller or larger planespacing) can then be actuated. The selection of the next Bragg gratingto actuate depends upon whether the desired wavelength of the firstactuated optical Bragg grating is more or less than the wavelength ofthe diffracted light. This adjustment or calibration process can beperformed either manually or by a computer using a comparison program,and can be performed continually during normal operation of an opticalsystem employing optical Bragg gratings.

FIG. 25 shows one embodiment of Echelle grating 2500. The Echellegrating 2500 may be used alternatively as a diffraction grating or alens grating depending on the biasing of the gate electrode. The Echellegrating 2500 is altered from the FIGS. 1 to 3 and 5 embodiment ofoptical waveguide device 100 by replacing the rectangular gate electrodeby a triangular-shaped Echelle gate electrode 2502. The Echelle-shapedgate electrode 2502 includes two parallel sides 2504 and 2506 (side 2506is shown as the point of the triangle, but actually is formed from alength of material shown in FIG. 26 as 2506), abase side 2510, and aplanar grooved surface 2512.

The base surface 2510 extends substantially perpendicular to theincident direction of travel of light (the light is indicated by arrows2606, 2607, and 2609 shown in FIG. 26) entering the Echelle grating. Thegrooved side 2512 is made of a series of individual grooves 2515 thatextend parallel to the side surface, and all of the grooves regularlycontinue from side 2504 to the other side 2506. Each groove 2515includes a width portion 2519 and rise portion 2517.

The rise portion 2517 defines the difference in distance that eachindividual groove rises from its neighbor groove. The rise portion 2517for all of the individual grooves 2515 are equal, and the rise portion2517 equals some integer multiple of the wavelength of the light that isto be acted upon by the Echelle grating 2500. Two exemplary adjacentgrooves are shown as 2515 a and 2515 b, so the vertical distance betweenthe grooves 2515 a and 2515 b equals 2517. The width portion 2519 of theEchelle shape gate electrode 2502 is equal for all of the individualgrooves. As such, the distance of the width portion 2519 multiplied bythe number of individual grooves 2515 equals the operational width ofthe entire Echelle shaped gate electrode. Commercially available threedimensional Echelle gratings that are formed from glass or asemiconductor material have a uniform cross section that is similar incontour to the Echelle shaped gate electrode 2502. The projected regionof changeable propagation constant 190 can be viewed generally incross-section as having the shape and dimensions of the gate electrode(including grooves), and extending vertically through the entirethickness of the waveguide 106. The numbers of individual grooves 2515in the FIG. 25 embodiment of Echelle shaped gate electrode 2502 mayapproach many thousand, and therefore, the size may become relativelysmall to provide effective focusing.

FIG. 26 shows the top cross sectional view of region of changeablepropagation constant 190 shaped as an Echelle grating 2500. Thewaveguide 106 is envisioned to be a slab waveguide, and is configured topermit the angular defraction of the beam of light emanating from theEchelle grating 2500. When voltages are applied to the FIG. 25embodiment of Echelle shaped gate electrode 2502, a projected region ofchangeable propagation constant 190 of the general shape shown in FIG.26 is established within the waveguide 106. Depending upon the polarityof the applied voltage to the Echelle shaped gate electrode in FIG. 25,the propagation constant within the projected region of changeablepropagation constant 190 can either exceed, or be less than, thepropagation constant within the waveguide outside of the projectedregion of changeable propagation constant 190. The relative level ofpropagation constants within the projected region of changeablepropagation constant 190 compared to outside of the projected region ofchangeable propagation constant determines whether the waveguide 106acts to diffract light or focus light. In this section, it is assumedthat the voltage applied to the gate electrode is biased so the Echellegrating acts to diffract light, although equivalent, techniques wouldapply for focusing light, and are considered a part of this disclosure.

In FIG. 26, three input light beams 2606, 2607, and 2609 extend into thewaveguide. The input light beams 2606, 2607, and 2609 are shown asextending substantially parallel to each other, and also substantiallyparallel to the side surface 2520 of the projected region of changeablepropagation constant 190. The projected region of changeable propagationconstant 190 as shown in FIG. 26 precisely mirrors the shape and size ofthe FIG. 25 embodiment of Echelle shaped gate electrode 2502. As such,the projected region of changeable propagation constant 190 can beviewed as extending vertically through the entire thickness of thewaveguide 106. The numbers of individual grooves 2515 in the FIG. 25embodiment of Echelle shaped gate electrode 2502 may approach manythousand to provide effective diffraction, and therefore, individualgroove dimensions are relatively small. It is therefore important thatthe projected region of changeable propagation constant 190 preciselymaps from the Echelle shaped gate electrode 2502.

Three input beams in 2606, 2607, and 2609 are shown entering theprojected region of changeable propagation constant 190, each containingmultiple wavelengths of light. The three input beams 2606, 2607, and2609 correspond respectively with, and produce, three sets of outputbeams 2610 a or 2610 b; 2612 a, 2612 b or 2612 c; and 2614 a or 2614 bas shown in FIG. 26. Each diffracted output beam 2610, 2612, and 2614 isshown for a single wavelength of light, and the output beam representsthe regions in which light of a specific wavelength that emanate fromdifferent grooves 2604 will constructively interfere. In otherdirections, the light destructively interferes.

The lower input light beam 2606 that enters the projected region ofchangeable propagation constant 190 travels for a very short distance d1through the projected region of changeable propagation constant 190(from the left to the right) and exits as output beam 2610 a or 2610 b.As such, though the region of changeable propagation constant 190 has adifferent propagation constant then the rest of the waveguide 106, theamount that the output beam 2610 a, or 2610 b is diffracted is verysmall when compared to the amount of diffraction of the other outputbeams 2612, 2614 that have traveled a greater distance through theprojected region of changeable propagation constant 190.

The middle input light beam 2607 enters the projected region ofchangeable propagation constant 190 and travels through a considerabledistance d2 before exiting from the Echelle grating. If there is novoltage applied to the gate electrode, then the output light will beunaffected by the region of changeable propagation constant 190 as thelight travels the region, and the direction of propagation for lightfollowing input path 2607 will be consistent within the waveguide along2612 a. If a voltage level is applied to the FIG. 25 embodiment of gateelectrode 2502, then the propagation constant within the region ofchangeable propagation constant 190 is changed from that outside theregion of changeable propagation constant. The propagation constant inthe region of changeable propagation constant 190 will thereupondiffract light passing from the input light beam 2607 through an angleθ_(d1) along path 2612 b. If the voltage is increased, the amount ofdiffraction is also increased to along the path shown at 2612 c.

Light corresponding to the input light beam 2609 will continue straightalong line 2614 a when no voltage is applied to the gate electrode. If aprescribed level of voltage is applied to the gate electrode, the outputlight beam will be diffracted through an output angle θ_(d2) alongoutput light beam 2614 b. The output angle θ_(d2) of output diffractedbeam 2614 b exceeds the output angle θ_(d1) of diffracted beam 2612 b.The output angle varies linearly from one side surface 2522 to the otherside surface 2520, since the output angle is a function of the distancethe light is travelling through the projected region of changeablepropagation constant 190.

When the Echelle grating diffracts a single wavelength of light throughan angle in which the waves are in phase, the waves of that lightconstructively interfere and that wavelength of light will becomevisible at that location. Light of different wavelength will notconstructively interfere at that same angle, but will at some otherangle. Therefore, in spectrometers, for instance, the location thatlight appears relates to the specified output diffraction angles of thelight, and the respective wavelength of the light within the light beamthat entered the spectrometer.

FIG. 27 shows one embodiment of Echelle grating 2700 that is configuredto reflect different wavelengths of light (instead of diffracting light)through an output reflection angle. For instance, an input light beam2702 of a prescribed wavelength, as it contacts a grating surface 2704of a projected Echelle grating 2706, will reflect an output light beam2708 through an angle. The propagation constant of the region ofchangeable propagation constant 190 will generally have to be higherthan that for a diffraction Echelle grating. In addition, the angle atwhich the grating surface 2704 faces the oncoming input light beam 2702would probably be lower if the light is refracted, not reflected. Suchdesign modifications can be accomplished by reconfiguring the shape ofthe gate electrode in the optical waveguide device. Shaping the gateelectrodes is relatively inexpensive compared with producing a distinctdevice.

3D Optical Lenses

Waveguide lenses are important devices in integrated optical circuitsbecause they can perform various essential functions such as focusing,expanding, imaging, and planar waveguide Fourier Transforms.

The FIG. 25 embodiment of Echelle grating 2500 can be used not only as adiffraction grating as described relative to FIG. 26, but the samestructure can also be biased to perform as a lens to focus light. To actas a lens, the polarity of the voltage of the Echelle grating 2500applied between the gate electrode and the combined first bodycontact/second body contact electrodes is opposite that shown for theFIGS. 26 embodiment of diffraction grating.

FIGS. 28 and 29 show three input light beams that extend into the regionof altered propagation constant 190 in the waveguide are shown as 2806,2807, and 2809. The input light beams 2806, 2807, and 2809 are shown asextending substantially parallel to each other, and also substantiallyparallel to the side surfaces 2520, 2522 of the projected region ofchangeable propagation constant 190. The projected region of changeablepropagation constant 190 shown in FIGS. 28 and 29 generally mirrorsvertically through the height of the waveguide the shape and size of theFIG. 25 embodiment of Echelle shaped gate electrode 2502.

The light input from the input beams 2806, 2807, and 2809 extend throughthe region of changeable propagation constant 190 to form, respectively,the three sets of output beams 2810 a and 2810 b; 2812 a, 2812 b and2812 c; and 2814 a and 2814 b as shown in FIG. 28. Each focused outputbeam 2810, 2812, and 2814 is shown for a single wavelength of light, andthe output beam represents the direction of travel of a beam of light ofa specific wavelength in which that beam of light will constructivelyinterfere. In other directions, the light of the specific wavelengthdestructively interferes.

The lower input light beam 2806 that enters near the bottom of theprojected region of changeable propagation constant 190 travels for avery short distance d1 through the projected region of changeablepropagation constant 190 (as shown from the left to the right) and exitsas output beam 2810 a or 2810 b. As such, though the region ofchangeable propagation constant 190 has a different propagation constantthen the rest of the waveguide 106. The amount that the output beam 2810a is focused is very small when compared to the amount of focusing onthe other output beams 2812, 2814 that have traveled a greater distancethrough the region of changeable propagation constant 190.

The middle input light beam 2807 enters the projected region ofchangeable propagation constant 190 and travels through a considerabledistance d2 before exiting from the projected Echelle grating. If thereis no voltage applied to the gate electrode, then the output light willbe unaffected by the region of changeable propagation constant 190, andlight following input path 2807 will continue straight after exiting thewaveguide along 2812 a. If a medium voltage level is applied to the gateelectrode, then the propagation constant within the region of changeablepropagation constant 190 will not equal that within the surroundingwaveguide. The propagation constant in the region of changeablepropagation constant 190 will deflect light beam 2807 through an angleθ_(f1) along path 2812 b. If the voltage is increased, the amount ofdeflection for focusing is also increased to the angle shown at 2812 c.

Light corresponding to the input light beam 2809 will continue straightthrough the region of changeable propagation constant along line 2814 awhen no voltage is applied to the gate electrode. If a prescribed levelof voltage is applied to the gate electrode, the output light beam willbe focused through an output angle θ_(f2) to along output light beam2814 b. The output angle θ_(f2) of output focused beam 2814 b exceedsthe output angle θ_(f1) of focused beam 2812 b if the same voltageapplied to the gate electrode. The output angle varies linearly from oneside surface 2522 to the other side 2520, since the output angle is afunction of the distance the light is travelling through the projectedregion of changeable propagation constant 190.

FIGS. 28 and 29 demonstrate that a voltage can be applied to an Echelleshaped gate electrode 2602, and that it can be biased in a manner tocause the Echelle grating 2500 to act as a focusing device. The level ofthe voltage can be varied to adjust the focal length. For example,assume that a given projected region of changeable propagation constant190 results in the output focused beams 2810, 2812, and 2814 convergingat focal point f_(P1). Increasing the gate voltage will cause thepropagation constant in the projected region of changeable propagationconstant 190 to increase, resulting in a corresponding increase in theoutput focus angle for each of the output focused beams. As such, theoutput focus beams would converge at a different point, e.g., at focalpoint f_(P2), thereby, effectively decreasing the focal length of thelens. The FIGS. 28 and 29 embodiment of focusing mechanism can be usedin cameras, optical microscopes, copy machines, etc., or any device thatrequires an optical focus. There are no moving parts in this device,which simplifies the relatively complex auto focus devices that arepresently required for mechanical lenses. Such mechanical autofocuslenses, for example, require precisely displacing adjacent lenses towithin a fraction of a wavelength.

FIG. 30 shows another embodiment of an optical waveguide device 100including a Bragg grating 3008 that is used as a lens to focus lightpassing through the waveguide. The embodiment of optical waveguidedevice 100, or more particularly the FIG. 2 embodiment of gate electrodeof the optical waveguide device, is modified by replacing the continuousgate electrode (in FIG. 2) with a discontinuous electrode in the shapeof a Bragg grating (shown in FIG. 30). The Bragg grating 3008 is formedwith a plurality of etchings 3010 that each substantially parallels theoptical path 101 of the optical waveguide device. In the FIG. 30embodiment of Bragg grating 3008, the thickness' of the successiveetchings to collectively form gate electrode 120 increase toward thecenter of the optical waveguide device, and decreases toward the edges120 a, 120 b of the gate electrode 120. Therefore, the region ofchangeable propagation constant 190 in the waveguide is thicker at thoseregions near the center of the waveguide. Conversely, the region ofchangeable propagation constant 190 becomes progressively thinner atthose regions of the waveguide near edges 120 a, 120 b. The propagationconstant is a factor of both the volume and the shape of the materialused to form the gate electrode. The propagation constant is thus higherfor those regions of changeable propagation constant closer to thecenter of the waveguide.

Light is assumed to be entering the waveguide 106 followingsubstantially parallel paths as shown by exemplary paths 3012 a and 3012b. Paths 3012 a and 3012 b represent two paths travelling at theoutermost positions of the waveguide. The locations between paths 3012 aand 3012 b are covered by a continuum of paths that follow similarroutes. When sufficient voltage is applied to the Bragg grating shapedelectrode, the light following paths 3012 a and 3012 b will be deflectedto follow output paths 3014 a and 3014 b, respectively. Output paths3014 a and 3014 b, as well as the paths of all the output paths thatfollow through the waveguide under the energized Bragg grating 3008 willbe deflected a slightly different amount, all toward a focus point 3016.The FIG. 30 embodiment of optical waveguide device therefore acts as alens. The Bragg grating 3008, though spaced a distance from thewaveguide, can be biased to direct the light in a manner similar to alens.

The reason why the embodiment of Bragg grating shown in FIG. 30 acts asa lens is now described. Light travelling within the waveguide requiresa longer time to travel across those regions of changeable propagationconstant at the center (i.e., taken vertically as shown in FIG. 30) thanthose regions adjacent the periphery of the lens (i.e., near edges 120a, 120 b). This longer time results because the propagation constant isgreater for those regions near the center. For light of a givenwavelength, light exiting the lens will meet at a particular focalpoint. The delay imparted on the light passing through the regions ofchangeable propagation constant nearer the center of the lens will bedifferent from that of the light passing near edges 120 a, 120 b. Thetotal time required for the light to travel to the focal point is madeup from the combination of the time to travel through the region ofchangeable propagation constant 190 added to the time to travel from theregion of changeable propagation constant 190 to the focal point. Thetime to travel through the region of changeable propagation constant 190is a function of the propagation constant of each region of changeablepropagation constant 190. The time to travel from the region ofchangeable propagation constant 190 to the focal point is a function ofthe distance from the region of changeable propagation constant 190 tothe focal point. As a result of the variation in propagation constantfrom the center of the waveguide toward the edges 120 a, 120 b, a givenwavelength of light arrives at a focal point simultaneously, and thelens thereby focuses light.

There has been increasing interest in waveguide lenses such as Fresnellenses and grating lenses. Such lenses offer limited diffractionperformance, and therefore they constitute a very important element inintegrated optic devices. Waveguide Fresnel lenses consist of periodicgrating structures that cause a spatial phase difference between theinput and the output wavefronts. The periodic grating structure gives awavefront conversion by spatially modulating the grating. Assuming thatthe phase distribution function of the input and output waves aredenoted by φ₁ and φ₂, respectively, the phase difference Δφ in theguided wave structure can be written as:Δφ=φ₀−φ₁  10

The desired wavefront conversion is achieved by a given phase modulationto the input wavefront equal to Δφ. The grating for such phasemodulation consists of grating lines described by:

 Δφ=2mπ  11

where m is an integer, and, for light having a specific wavelength, thelight from all of the grating lines will interfere constructively.

The phase difference Δφ for a planar waveguide converging wave followsthe expression:Δφ(x)=kn _(eff)(f−√{square root over (x ² +f ² )})  12

where f is the focal length, n_(eff) is the propagation constant of thewaveguide, and x is the direction of the spatial periodic gratingmodulation.

FIGS. 30 and 31 show two embodiments of optical waveguide devices thatperform waveguide Fresnel lens functions. The two-dimensional Fresnellenses follow the phase modulation like their three-dimensional lenscounterpart:φ_(F)(x)=Δφ(x)+2mπ  13

for x_(m)<|x|<x_(m+1), the phase modulation Δφ(x_(m))=2mπ, which isobtained by segmenting the modulation into Fresnel zones so thatφ_(F)(x) has amplitude 2π. Under the thin lens approximation, the phaseshift is given by KΔnL. Therefore, the phase of the wavefront for aspecific wavelength can be controlled by the variations of Δn and L. IfΔn is varied as a function of x, where the lens thickness, L, is heldconstant, as shown in FIG. 30, it is called the GRIN Fresnel lens and isdescribed by:Δn(x)=Δn _(max)(φ_(F)(x)/2π+1)  14

FIG. 32 shows one embodiment of optical waveguide device that operatesas a gradient-thickness Fresnel lens where Δn is held constant. Thethickness of the lens L has the following functional form:L(x)=L _(max)(φ_(F)(x)/2π+1)  15

To have 2π phase modulation, in either the FIG. 30 or FIG. 31 embodimentof lens, the modulation amplitude must be optimized. The binaryapproximation of the phase modulation results in the step-index Fresnelzone lens. The maximum efficiency of 90%, limited only by diffraction,can be obtained in certain lenses.

Another type of optical waveguide device has been designed by spatiallychanging the K-vector as a function of distance to the central axis,using a so-called chirped Bragg grating configuration. In chirped Bragggrating configurations, the cross sectional areas of the region ofchangeable propagation constant 190 are thicker near the center of thewaveguide than the periphery to provide a greater propagation constantas shown in the embodiment of FIG. 30. Additionally, the output of eachregion of changeable propagation constant 190 is angled towards thefocal point to enhance the deflection of the light toward the deflectionpoint. The architecture of the FIG. 32 embodiment of chirped Bragggrating waveguide lens results in index modulation according to theequation:Δn(x)=Δn cos [Δφ(x)]=Δn cos {Kn _(e) [Kn _(e)(f−√x ² +f)]}  16

Where f=focal length, Δφ=phase difference; L is the lens thickness ofthe Bragg grating; x is the identifier of the grating line, and n is therefractive index. As required by any device based on grating deflection,the Q parameter needs to be greater than 10 to reach the Bragg region inorder to have high efficiency. The grating lines need to be gradientlyslanted following the expression:Ψ(x)=½ tan⁻¹(x/f)≅x/2f  17

so that the Bragg condition is satisfied over the entire aperture. Thecondition for maximum efficiency is:

 kL=πΔnL/λ=π2  18

In the embodiment of the optical waveguide device as configured in FIG.32, adjustments may be made to the path length of the light passingthrough the waveguide by using a gate electrode formed with compensatingprism shapes. Such compensating prism shapes are configured so that thevoltage taken across the gate electrode (from the side of the gateelectrode adjacent the first body contact electrode to the side of thegate electrode adjacent the second body contact electrode) varies. Sincethe voltage varies across the gate electrode vary, the regions ofchangeable propagation constant will similarly vary across the width ofthe waveguide. Such variation in the voltage will likely result in agreater propagation of the light passing through the waveguide atdifferent locations across the width of the waveguide.

FIG. 33 shows a front view of another embodiment of optical waveguidedevice from that shown in FIG. 1. The optical waveguide device 100 shownin FIG. 33 is configured to operate as a lens 3300. The depth of theelectrical insulator layer 3302 varies from a maximum depth adjacent theperiphery of the waveguide to a minimum depth adjacent the center of thewaveguide. Due to this configuration, a greater resistance is providedby the electrical insulator 3302 to those portions that are adjacent theperiphery of the waveguide and those portions that are the center of thewaveguide. The FIG. 33 embodiment of optical lens can establish apropagation constant gradient across the width of the waveguide. Thevalue of the propagation constant will be greatest at the center, andlesser at the periphery of the waveguide. This embodiment of lens 3300may utilize a substantially rectangular gate electrode. It may also benecessary to provide one or more wedge shape spacers 3306 that are madefrom material having a lower electrical resistance than the electricalinsulator 3302 to provide a planer support surface to support the gateelectrode. Other similar configurations in which the electricalresistance of the electrical insulator is varied to provide a variedelectrical field at the insulator/semiconductor interface and a variedpropagation constant level.

3E. Optical Filters

The optical waveguide device 100 can also be modified to provide avariety of optical filter functions. Different embodiments of opticalfilters that are described herein include an arrayed waveguide (AWG)component that acts as a multiplexer/demultiplexer or linear phasefilter in which a light signal can be filtered into distinct bandwidthsof light. Two other embodiments of optical filters are afinite-impulse-response (FIR) filter and an infinite-impulse-response(IIR) filter. These embodiments of filters, as may be configured withthe optical waveguide device, are now described.

FIG. 34 shows one embodiment of an optical waveguide device beingconfigured as an AWG component 3400. The AWG component 3400 may beconfigured to act as a wavelength multiplexer, wavelength demultiplexer,a linear phase filter, or a router. The AWG component 3400 is formed ona substrate 3401 with a plurality of optical waveguide devices. The AWGcomponent 3400 also includes an input waveguide 3402 (that may be formedfrom one waveguide or an array of waveguides for more than one inputsignal), an input slab coupler 3404, a plurality of arrayed waveguidedevices 3410, an output slab coupler 3406, and an output waveguide array3408. The input waveguide 3402 and the output waveguide array 3408 eachcomprise one or more channel waveguides (as shown in the FIGS. 1 to 3,4, or 5 embodiments) that are each optically coupled to the input slabcoupler 3402. Slab couplers 3404 and 3406 allow the dispersion of light,and each slab coupler 3404 and 3406 may also be configured as in theFIGS. 1 to 3 or 5 embodiments. Each one of the array waveguides 3410 maybe configured as in the FIGS. 10 to 11 embodiment of channel waveguide.Controller 201 applies a variable DC voltage V_(g) to some or all of thewaveguide couplers 3402, 3404, 3406, 3408, and 3410 to adjust forvariations in temperature, device age and characteristics, or otherparameters as discussed above in connection with the FIGS. 7-8. In theembodiment shown, controller 201 does not have to apply an alternatingcurrent signal v_(g) to devices 3402, 3404, 3406, 3408, and 3410.

The input array 3402 and the input slab coupler 3404 interact to directlight flowing through one or more of the input waveguides of the channelwaveguides 3410 depending upon the wavelength of the light. Each arraywaveguide 3410 is a different length, and can be individually modulatedin a manner similar to described above. For example, the upper arraywaveguides, shown with the greater curvature, have a greater light pathdistance than the lower array waveguides 3410 with lesser curvature. Thedistance that light travels through each of the array waveguides 3410differs so that the distance of light exiting the different arraywaveguides, and the resultant phase of the light exiting from thedifferent array waveguides, differ.

Optical signals pass through the plurality of waveguides (of the channeland slab variety) that form the AWG component 3400. The AWG component3400 is often used as an optical wavelength divisiondemultiplexer/multiplexer. When the AWG component 3400 acts as anoptical wavelength division demultiplexer, one input multi-bandwidthsignal formed from a plurality of input component wavelength signals ofdifferent wavelengths is separated by the AWG component 3400 into itscomponent plurality of output single-bandwidth signals. The inputmulti-bandwidth signal is applied to the input waveguide 3402 and theplurality of output single-bandwidth signals exit from the outputwaveguide array 3408. The AWG component 3400 can also operate as amultiplexer by applying a plurality of input single-bandwidth signals tothe output waveguide array 3408 and a single output multi-bandwidthsignal exits from the input waveguide 3402.

When the AWG component 3400 is configured as a demultiplexer, the inputslab coupler 3404 divides optical power of the input multi-bandwidthsignal received over the input waveguide 3402 into a plurality of arraysignals. In one embodiment, each array signal is identical to each otherarray signal, and each array signal has similar signal characteristicsand shape, but lower power, as the input multi-bandwidth signal. Eacharray signal is applied to one of the plurality of arrayed waveguidedevices 3410. Each one of the plurality of arrayed waveguide devices3410 is coupled to the output terminal of the input slab coupler 3404.The AWG optical wavelength demultiplexer also includes the output slabcoupler 3406 coupled to the output terminal of the plurality of arrayedwaveguide devices 3410. Each arrayed waveguide device 3410 is adapted toguide optical signals received from the input slab coupler 3404 so eachone of the plurality of arrayed waveguide signals within each of therespective plurality of arrayed waveguide devices (that is about to exitto the output slab coupler) has a consistent phase shift relative to itsneighboring arrayed waveguides device 3410. The output slab coupler 3406separates the wavelengths of each one of the arrayed waveguide signalsoutput from the plurality of arrayed waveguide devices 3410 to obtain aflat spectral response.

Optical signals received in at least one input waveguide 3402 passthrough the input slab coupler 3404 and then enter the plurality ofarrayed waveguide devices 3410 having a plurality of waveguides withdifferent lengths. The optical signals emerging from the plurality ofarrayed waveguide devices 3410 have different phases, respectively. Theoptical signals of different phases are then incident to the output slabcoupler 3406 in which a reinforcement and interference occurs for theoptical signals. As a result, the optical signals are focused at one ofthe output waveguide array 3408. The resultant image is then outputtedfrom the associated output waveguide array 3408.

AWG optical wavelength demultiplexers are implemented by an arrayedwaveguide grating configured to vary its wavefront direction dependingon a variation in the wavelength of light. In such AWG opticalwavelength demultiplexers, a linear dispersion indicative of a variationin the shift of the main peak of an interference pattern on a focalplane (or image plane) depending on a variation in wavelength can beexpressed as follows: $\begin{matrix}{\frac{\mathbb{d}_{x}}{\mathbb{d}\lambda} = \frac{fm}{n_{s}d}} & 19\end{matrix}$

where “f” represents the focal distance of a slab waveguide, “m”represents the order of diffraction, “d” represents the pitch of one ofthe plurality of arrayed waveguide devices 3410, and “n_(s)” is theeffective refractive index of the slab waveguide. In accordance withequation 19, the wavelength distribution of an optical signal incidentto the AWG optical wavelength demultiplexer is spatially focused on theimage plane of the output slab coupler 3406. Accordingly, where aplurality of output waveguides in array 3408 are coupled to the imageplane while being spaced apart from one another by a predetermineddistance, it is possible to implement an AWG optical wavelengthdemultiplexer having a wavelength spacing determined by the location ofthe output waveguide array 3408.

Optical signals respectively outputted from the arrayed waveguides ofthe AWG component 3400 while having different phases are subjected to aFraunhofer diffraction while passing through the output slab coupler3406. Accordingly, an interference pattern is formed on the image planecorresponding to the spectrum produced by the plurality of outputsingle-bandwidth signals. The Fraunhofer diffraction relates the inputoptical signals to the diffraction pattern as a Fourier transform.Accordingly, if one of the input multi-bandwidth signals is known, it isthen possible to calculate the amplitude and phase of the remaininginput multi-bandwidth signals using Fourier transforms.

It is possible to provide phase and/or spatial filters that filter theoutput single-bandwidth signals that exit from the output waveguidearray 3408. U.S. Pat. No. 6,122,419 issued on Sep. 19, 2000 to Kurokawaet al. (incorporated herein by reference) describes different versionsof such filtering techniques.

FIG. 35 shows one embodiment of a finite-impulse-response (FIR) filter3500. The FIR filter 3500 is characterized by an output that in a linearcombination of present and past values of inputs. In FIG. 35, x(n) showsthe present value of the input, and x(n−1), x(n−2), etc. represent therespective previous values of the input; y(x) represents the presentvalue of the output; and h(1), h(2) represent the filter coefficients ofx(n), y(n−1), etc. The D corresponds to the delay. The FIR filter 3500satisfies equation 20: $\begin{matrix}{y = {\sum\limits_{k = 0}^{M}{{h(k)}{x\left( {n - k} \right)}}}} & 20\end{matrix}$

An AWG, for example, is one embodiment of FIR filter in which thepresent output is a function entirely of past input. One combination ofoptical waveguide devices, a top view of which is shown in FIG. 36, is aFIR filter 3600 known as a coupled waveguide 3600. The coupled waveguide3600, in its most basic form, includes a first waveguide 3602, a secondwaveguide 3604, a coupling 3606, and a light pass grating 3608. Thefirst waveguide 3602 includes a first input 3610 and a first output3612. The time necessary of light to travel through the first waveguide3602 and/or the second waveguide 3604 corresponds to the delay D shownin the FIG. 35 model of FIR circuit. The second waveguide 3604 includesa second input 3614 and a second output 3616.

The coupling 3606 allows a portion of the signal strength of the lightflowing through the first waveguide 3602 to pass into the secondwaveguide 3604, and vice versa. The amount of light flowing between thefirst waveguide 3602 and the second waveguide 3604 via the coupling 3606corresponds to the filter coefficients h(k) in equation 20. Oneembodiment of light pass grating 3608 is configured as a Bragg gratingas shown in FIGS. 20 to 22. Controller 201 varies the gate voltage ofthe light pass grating to control the amount of light that passesbetween the first waveguide 3602 and the second waveguide 3604, andcompensates for variations in device temperature. An additional coupling3606 and light pass grating 3608 can be located between each additionalpair of waveguides that have a coefficient as per equation 20.

FIG. 37 shows one embodiment of a timing model of aninfinite-impulse-response (IIR) filter 3700. The FIG. 37 model of IIRfilter is characterized by an output that is a linear combination of thepresent value of the input and past values of the output. The IIR filtersatisfies equation 21: $\begin{matrix}{{y(n)} = {{x(n)} + {\sum\limits_{k = 1}^{M}{\alpha_{k}{y\left( {n - k} \right)}}}}} & 21\end{matrix}$

Where x(n) is a present value of the filter input; y(n) is the presentvalue of the filter output; y(n−1), etc. are past values of the filteroutput; and α₁, . . . , α_(M) are the filter coefficients.

One embodiment of an IIR filter 3800 is shown in FIG. 38. The IIR filter3800 includes an input waveguide 3801, a combiner 3802, a waveguide3803, an optical waveguide device 3804, a waveguide 3805, a beamsplitter 3806, an output waveguide 3807, and a delay/coefficient portion3808. The delay/coefficient portion 3808 includes a waveguide 3809, avariable optical attenuator (VOA) 3810, and waveguide 3812. Thedelay/coefficient portion 3808 is configured to provide a prescribedtime delay to the optical signals passing from the beam splitter 3806 tothe combiner 3802. In the FIG. 38 embodiment of an IIR filter 3800, Thetime necessary for light to travel around a loop defined by elements3802, 3803, 3804, 3805, 3806, 3809, 3810, and 3812 once equals the delayD shown in the FIG. 37 model of IIR circuit. The variable opticalattenuator 3810 is configured to provide a prescribed amount of signalattenuation to correspond to the desired coefficient, α₁ to α_(M). Anexemplary VOA is described in connection with FIG. 41 below.

Input waveguide 3801 may be configured, for example, as the channelwaveguide shown in FIGS. 1 to 3, 4, or 5. Combiner 3802 may beconfigured, for example, as a Bragg grating shown in FIGS. 20 to 22integrated in a slab waveguide shown in the FIGS. 1 to 3, 4, or 5. Thewaveguide 3803 may be configured, for example, as the channel waveguideshown in FIGS. 1 to 3, 4, or 5. The optical waveguide device 3804 may beconfigured, for example, as the channel waveguide shown in FIGS. 1 to 3,4, or 5. The waveguide 3805 may be configured, for example, as thechannel waveguide shown in FIGS. 1 to 3, 4, or 5. The beam splitter 3806may be configured, for example, as the beamsplitter shown below in FIG.46. The waveguide 3809 may be configured, for example, as the channelwaveguide shown in FIGS. 1 to 3, 4, or 5. The VOA 3810 may be configuredas shown below relative to FIG. 41. The waveguide 3812 may beconfigured, for example, as the channel waveguide shown in FIGS. 1 to 3,4, or 5.

Controller 201 applies a variable DC voltage V_(g) to the respectivegate electrodes of the input waveguide 3801, the combiner 3802, thewaveguide 3803, the optical waveguide device 3804, the waveguide 3805,the beam splitter 3806, the waveguide 3809, the VOA 3810, and thewaveguide 3812 to adjust for variations in temperature, device age,device characteristics, etc. as discussed below in connection with FIGS.7-8. In addition, controller 201 also varies the gate voltage applied toother components of the IIR to vary their operation, as discussed below.

During operation, an optical signal is input into the waveguide 3801.Virtually the entire signal strength of the input optical signal flowsthrough the combiner 3802. The combiner 3802 is angled to a sufficientdegree, and voltage is applied to a sufficient amount so the propagationconstant of the waveguide is sufficiently low to allow the light fromthe waveguide 3801 to pass directly through the combiner 3802 to thewaveguide 3803. The majority of the light that passes into waveguide3803 continues to the optical waveguide device 3804. The opticalwaveguide device 3804 can perform a variety of functions upon the light,including attenuation and/or modulation. For example, if it is desiredto input digital signals, the optical waveguide device 3804 can bepulsed on and off as desired when light is not transmitted to the outputwaveguide 3807 by varying the gate voltage of waveguide device 3804. Ifthe optical waveguide device 3804 is turned off and is fullyattenuating, then a digital null signal will be transmitted to theoutput waveguide 3807.

The output signal from the output waveguide device 3804 continuesthrough waveguide 3805 into beam splitter 3806. Beam splitter 3806diverts a prescribed amount of the light into waveguide 3809, and alsoallows prescribed amount of the light to continue onto the outputwaveguide 3807. The voltage applied to the gate of the beam splitter3806 can be changed by controller 201 to control the strength of lightthat is diverted to waveguide 3809 compared to that that is allowed topass to output waveguide 3807.

The light that is diverted through waveguide 3809 continues through thevariable optical attenuator 3810. The voltage applied to the variableoptical attenuator (VOA) 3810 can be adjusted depending upon the desiredcoefficient. For example, full voltage applied to the gate electrode ofthe VOA 3810 would fully attenuate the light passing through thewaveguide. By comparison, reducing the voltage applied to the gateelectrode would allow light to pass through the VOA to the waveguide3812. Increasing the amount of light passing through the VOA acts toincrease the coefficient for the IIR filter corresponding to thedelay/coefficient portion 3808. The light that passes through to thewaveguide 3812 continues on to the combiner 3802, while it is almostfully deflected into waveguide 3803 to join the light that is presentlyinput from the input waveguide 3801 through the combiner 3802 to thewaveguide 3803. However, the light being injected from waveguide 3812into the combiner 3803 is delayed from the light entering from the inputwaveguide 3801. A series of these IIR filters 3800 can be arrangedserially along a waveguide path.

FIGS. 39 and 40 show two embodiments of a dynamic gain equalizer thatacts as a gain flattening filter. The structure and filtering operationof the dynamic gain equalizer is described below.

3F. Variable Optical Attenuators

A variable optical attenuator (VOA) is used to controllable attenuateone or more bandwidths of light. The VOA is embodiment of opticalamplitude modulators, since optical attenuation may be considered a formof amplitude modulation. FIG. 41 shows one embodiment of a VOA 4100 thatis modified from the FIGS. 1 to 3 or 5 embodiment of optical waveguidemodulators. The VOA 4100 includes multiple sets of patterned Bragggratings 4102 a, 4102 b, and 4102 c, multiple gate electrodes 4104 a,4104 b, and 4104 c, multiple variable voltage sources 4106 a, 4106 b,and 4106 c, and a monitor 4108. Each individual plane in the patternedBragg gratings 4102 a, 4102 b, and 4102 c are continuous even throughthey are depicted using dotted lines (since they are located behind, oron the backside of, the respective gate electrodes 4104 a, 4104 b, and4104 c).

Each of the multiple sets of patterned Bragg gratings 4102 a, 4102 b,and 4102 c correspond, for example, to the embodiments of Bragg gratingshown in FIGS. 20-22, and may be formed in the electrical insulatorlayer or each respective gate electrode. The respective gate electrode4104 a, 4104 b, or 4104 c, or some insulative pattern is provided asshown in the FIGS. 20 to 22 embodiments of Bragg gratings. In any one ofthe individual patterned Bragg gratings 4102 a, 4102 b, and 4102 c, thespacing between adjacent individual gratings is equal. However, thespacing between individual adjacent gratings the FIG. 41 embodiment ofpatterned Bragg gratings 4102 a, 4102 b, and 4102 c decreases from thelight input side to light output side (left to right). Since the gratingsize for subsequent patterned Bragg gratings 4102 a, 4102 b, and 4102 cdecreases, the wavelength of light refracted by each also decreases frominput to output.

Each patterned Bragg gratings 4102 a-4102 c has a variable voltagesource applied between its respective gate electrode 4104 a, 4104 b, and4104 c and its common voltage first body contact electrode/second bodycontact electrode. As more voltage is applied between each of thevariable voltage sources 4106 a, 4106 b, and 4106 c and the Bragggratings 4102 a to 4102 c, the propagation constant of that patternedBragg grating increases. Consequently, more light of the respectivewavelengths λ₁, λ₂,or λ₃ associated with the spacing of that patternedBragg gratings 4102 a to 4102 c would be refracted, and interfereconstructively. The monitor 4108 can monitor such light that interferesconstructively.

Depending upon the intensity of the refracted light at each wavelength,equation 22 applies.P _(R)(λ₁)+P _(T)(λ₁)=P ₀(λ₁)  22

where P_(R)(λ₁) equals the refracted light, P_(T)(λ₁) equals thetransmitted light, and P_(o)(λ₁) equals the output light. In a typicalembodiment, a variable optical attenuator 4100 may be arranged with,e.g., 50 combined patterned Bragg gratings and gate electrodes (thoughonly three are shown in FIG. 41). As such, light having 50 individualbandwidths could be attenuated from a single light beam using thevariable optical attenuator 4100.

3G. Programmable Delay Generators and Optical Resonators

Programmable delay generators are optical devices that add a prescribed,and typically controllable, amount of delay to an optical signal.Programmable delay generators are used in such devices asinterferometers, polarization control, and optical interferencetopography that is a technology used to examine eyes. In all of thesetechnologies, at least one optical signal is delayed. FIG. 42 shows atop view of one embodiment of a programmable delay generator 4200. FIG.43 shows a side cross sectional view of the FIG. 42 embodiment ofprogrammable delay generator 4200. In addition to the standardcomponents of the optical waveguide device shown in the embodiments ofFIGS. 1-3, 4, or 5, the programmable delay generator 4200 includes aplurality of Bragg grating devices 4202 a to 4202 e and a plurality ofaxially arranged gate electrodes 120. The embodiment of Bragg gratingsdevices 4202 shown in FIGS. 42 and 43 are formed in the lower surface ofthe gate electrode, however, the Bragg grating devices may alternativelybe formed as shown in the embodiments in FIGS. 20 to 22 as grooves inthe lower surface of the electrical insulator, as insulator elementshaving different resistance inserted in the insulator, as grooves formedin the lower surface of the gate electrode, or as some equivalent Braggstructure such as using surface acoustic waves that, as with the otherBragg gratings, project a series of parallel planes 4204, representingregions of changeable propagation constant, into the waveguide. Thespacing between the individual grooves in the Bragg grating equals somemultiple of the wavelength of light that to be reflected.

Each axially arranged gate electrode 120 is axially spaced a shortdistance from the adjacent gate electrodes, and the spacing depends uponthe amount by which the time delay of light being reflected within theprogrammable delay generator 4200 can be adjusted. During operation, agate voltage is applied to one of the axially arranged gate electrodes120 sufficient to increase the strength of the corresponding region ofchangeable propagation constant sufficiently to reflect the lighttravelling within the optical waveguide device.

As shown in FIG. 43, the gate electrode from Bragg grating device 4202 cis energized, so incident light path 4302 will reflect off the region ofchangeable propagation constant 190 associated with that gate electrodeand return along return light path 4304. The delay applied to lighttravelling within the channel waveguide is therefore a function of thelength of the channel waveguide between where light is coupled intoand/or removed from the channel waveguide and where the actuated gateelectrode projects its series of planes or regions of changeablepropagation constant. The light has to travel the length of the incidentpath and the return path, so the delay provided by the programmabledelay generator generally equals twice the incident path length dividedby the speed of light. By electronically controlling which of the Bragggrating devices 4202 a to 4202 e are actuated at any given time, thedelay introduced by the delay generator 4200 can be dynamically varied.

In one embodiment of operation for the programmable delay generator4200, only one axially arranged gate electrode 120 is energized withsufficient strength to reflect all the light since that electrode willreflect all of the light travelling within the waveguide. Thisembodiment provides a so-called hard reflection since one plane orregions of changeable propagation constant reflects all of the incidentlight to form the return light.

In another embodiment of operation for the programmable delay generator4200, a plurality of adjacent, or axially spaced as desired, gateelectrodes 120 are energized using some lesser gate voltage level thanapplied in the prior embodiment to reflect all of the light. The planesor regions of changeable propagation constant associated with eachactuated axially arranged gate electrode 120 each reflect somepercentage of the incident light to the return light path. The latterembodiment uses “soft” reflection since multiple planes or regions ofchangeable propagation constant reflect the incident light to form thereturn light.

Optical resonators are used to contain light within a chamber (e.g. thechannel waveguide) by having the light reflect between optical mirrorslocated at the end of that waveguide. The FIG. 44 embodiment ofresonator 4400 is configured as a channel waveguide so the light isconstrained within two orthogonal axes due to the total internalreflectance (TIR) of the channel waveguide. Light is also constrainedalong the third axis due to the positioning of TIR mirrors at eachlongitudinal end of the waveguide. The optical resonator 4400 forms atype of Fabry-Perot resonator. Resonators, also known as opticalcavities, can be integrated in such structures as lasers.

The resonator 4400 includes a optical waveguide of the channel type, oneor more input mirror gate electrodes 4402, one or more output mirrorgate electrodes 4404, and controllable voltage sources 4406 and 4408that apply voltages to the input mirror gate electrodes 4402 and theoutput mirror gate electrodes 4404, respectively. FIG. 45 shows a topview of the channel waveguide of the resonator 4400 of FIG. 44. Thechannel waveguide includes, when the voltage sources 4406 and/or 4408are actuated, an alternating series of high propagation constant bands4502 and low propagation constant bands 4504.

The high propagation constant bands 4502 correspond to the location ofthe input mirror gate electrodes 4402 or the output mirror gateelectrodes 4404. The low propagation constant bands 4504 correspond tothe bands between the input mirror gate electrodes 4402 or the outputmirror gate electrodes 4404. The high propagation constant bands 4502and the low propagation constant bands 4504 extend vertically throughthe waveguide. The input mirror gate electrodes 4402 and the outputmirror gate electrodes 4404 can be shaped to provide, e.g., a concavemirror surface if desired. Additionally, deactuation of the input mirrorgate electrodes 4402 or the output mirror gate electrodes 4404 removesany effect of the high propagation constant bands 4502 and lowpropagation constant bands 4504 from the waveguide of the resonator4400; Such effects are removed since the propagation constant approachesa uniform level corresponding to 0 volts applied to the gate electrodes4502, 4504.

As light travels axially within the waveguide of the resonator 4400,some percentage of the light will reflect off any one of one or morejunctions 4510 between each high propagation constant band 4502 and theadjacent low propagation constant band 4504, due to the reducedpropagation constant. Reflection off the junctions 4510 between highindex areas and low index areas forms the basis for much of thin filmoptical technology. The junction 4510 between each high propagationconstant band 4502 and the adjacent low propagation constant band 4504can be considered analogous to Bragg gratings. The greater the numberof, and the greater the strength of, such junctions 4510, the more lightthat will be reflected from the respective input mirror gate electrodes4402 or the output mirror gate electrodes 4404. Additionally, thegreater the voltage applied from the controllable voltage sources 4406and 4408 to the respective input mirror gate electrodes 4402 or theoutput mirror gate electrodes 4404, the greater the difference inpropagation constant between the high propagation constant band 4502 andthe adjacent low propagation constant band 4504 for the respective inputmirror gate electrodes 4402 or the output mirror gate electrodes 4404.

FIG. 46 shows a top view of one embodiment of beamsplitter 4600 that isformed by modifying the optical waveguide device 100 shown in FIG. 46.The beamsplitter includes an input mirror 4602 having a first face 4604and a second face 4606. The mirror 4602 may be established in thewaveguide in a similar manner to a single raised land to provide avaried electrical field at the insulator/semiconductor interface in oneof the embodiments of Bragg gratings shown in FIGS. 20 to 22. Thevoltage level applied to the gate electrode 120 is sufficient toestablish a relative propagation constant level in the region ofchangeable propagation constant to reflect a desired percentage of lightfollowing incident path 101 to follow path 4610. The region ofchangeable propagation constant takes the form of the mirror 4602. Lightfollowing incident path 101 that is not reflected along path 4610continues through the mirror 4602 to follow the path 4612. Such mirrors4602 also reflect a certain percentage of return light from path 4612 tofollow either paths 4614 or 101. Return light on path 4610 thatencounters mirror 4602 will either follow path 101 or 4614. Return lighton path 4614 that encounters mirror 4602 will either follow path 4612 orpath 4610. The strength of the voltage applied to the gate electrode 120and the resulting propagation constant level of the region of changeablepropagation constant in the waveguide, in addition to the shape and sizeof the mirror 4602 determine the percentage of light that is reflectedby the mirror along the different paths 101, 4610, 4612, and 4614.

3H. Optical Application Specific Integrated Circuits (OASICS)

Slight modifications to the optical functions and devices such asdescribed in FIGS. 16 to 25, taken in combination with free-carrierbased active optics, can lead to profound changes in optical designtechniques. Such modifications may only involve minor changes to thestructure of the gate electrode.

The optical waveguide device may be configured as a variable opticalattenuator that changes voltage between the gate electrode, the firstbody contact electrode, and the second body contact electrode, such thata variable voltage is produced across the width of the waveguide. Thisconfiguration results in a variable attenuation of the light flowingthrough the waveguide across the width of the waveguide.

If a magnetic field is applied to the 2DEG, then the free-carriersexhibit birefringence. The degree of birefringence depends on themagnitude of the magnetic field, the free-carrier or 2DEG density, andthe direction of propagation of the optical field relative to themagnetic field. The magnetic field may be generated by tarditionalmeans, i.e. from passing of current or from a permanent magnet. Themagnetic field induced birefringence can be harnessed to make variousoptical components including polarization retarders, mode couplers, andisolators.

IV. Integrated Optical Circuits Including Optical Waveguide Devices

4A. Introduction to Integrated Optical Circuits

The optical functions of the optical waveguide devices described abovecan be incorporated onto one (or more) chip(s) in much the same way asone currently designs application specific integrated circuits (ASICS)and other specialized electronics, e.g., using standard libraries andspice files from a foundry. The optical functions of the opticalwaveguide devices described herein can be synthesized and designed inmuch the same way as electronic functions are, using ASICS. One may usean arithmetic logic unit (ALU) in a similar manner that ASICS arefabricated. This level of abstraction allowed in the design of opticalcircuits by the use of optical waveguide devices improves the capabilityof circuit designers to create and fabricate such large scale andinnovative designs as have been responsible for many of thesemiconductor improvements in the past.

As discussed above, different devices can be constructed by modifyingthe basic structure described in FIG. 1 by, e.g. changing the shape,configuration, or thickness of the gate electrode. These modifieddevices can provide the building blocks for more complex circuits, in asimilar manner that semiconductor devices form the basic building blocksfor more complex integrated circuit structures.

The disclosure now describes a variety of integrated optical circuitsthat can be constructed using a plurality of optical waveguide devicesof the type described above. The integrated optical circuits describedare illustrative in nature, and not intended to be limiting in scope.Following this description, it becomes evident that the majority offunctions that are presently performed by using current integratedcircuits can also be formed using integrated optical circuits. Theadvantages are potential improvement in operating circuit capability,cost, and power consumption. It is to be understood that certain ones ofthe functions shown as being performed by an active optical waveguidedevice in the following integrated optical circuits may also beperformed using a passive device. For example, devices 4708 and 4712 inthe embodiment shown in FIG. 47 may be performed by either activedevices or passive devices. The embodiment of beamsplitter 4600 shown inFIG. 46 can either be an active or passive device. The selection ofwhether to use an active or passive device depends, e.g., on theoperation of the integrated optical circuit with respect to eachparticular optical waveguide device, and the availability of eachoptical waveguide device in active or passive forms.

It is emphasized that the multiple optical waveguide devices of thetypes described above relative to FIGS. 1-3, 4, or 5 may be combined indifferent ways to form the following described integrated opticalcircuits shown, for example, in the embodiments of FIGS. 18, 19, 34, 36,38-45, and 47-49. For example, the different integrated optical circuitembodiments may be formed using a plurality of optical waveguide devicesformed on a single substrate. More particularly, the differentembodiments of integrated optical circuits may comprise multiple opticalwaveguide devices attached to different portions of a single waveguide.Alternatively, the different embodiments of integrated optical circuitsincluding multiple optical waveguide devices may be formed on aplurality of discrete optical waveguide devices.

4B. Dynamic Gain Equalizer

FIG. 39 shows one embodiment of a dynamic gain equalizer 3900 comprisinga plurality of optical waveguide devices. The dynamic gain equalizer3900 comprises a wavelength separator 3902 (that may be, e.g. an arrayedwaveguide or an Echelle grating), a beam splitter 3904, a monitor 3906,the controller 201, a variable optical attenuator bank 3910, a wavelength combiner 3912, and an amplifier 3914. Dynamic gain equalizers arecommonly used to equalize the strength of each one of a plurality ofsignals that is being transmitted over relatively long distances. Forexample, dynamic gain equalizers are commonly used in long distanceoptical telephone cables and a considerable portion of the signalstrength is attenuated due to the long transmission distances between,e.g., states or countries.

The wavelength separator 3902 acts to filter or modulate the wavelengthof an incoming signal over waveguide 3916 into a plurality of lightsignals. Each of these light signals has a different frequency. Each ofa plurality of waveguides 3918 a to 3918 d contain a light signal ofdifferent wavelength λ₁ to λ_(n) the wavelength of each signalcorresponds to a prescribed limited bandwidth. For example, waveguide3918 a carries light having a color corresponding to wavelength λ₁,while waveguide 3918 carries a light having a color corresponding towavelength λ₂, etc.

Each of the waveguides 3918 a to 3918 d is input into the beam splitter3904. The beam splitter outputs a portion of its light into a variableoptical attenuator 3910, and also deflects a portion of its light to themonitor 3906. The monitor 3906 senses the proportional signal strengththat is being carried over waveguide 3918 a to 3918 d. Both the monitor3906 and the beam splitter 3904 may be constructed using the techniquesfor the optical waveguide devices described above. The controller 201receives a signal from the monitor that indicates the signal strength ofeach monitored wavelength of light being carried over waveguides 3918 ato 3918 d.

The controller monitors the ratios of the signal strengths of thedifferent wavelength bands of light carried by waveguides 3918 a to 3918d, and causes a corresponding change in the operation of the variableoptical attenuator bank 3910. The variable optical attenuator bank 3910includes a plurality of variable optical attenuators 3930 a, 3930 b,3930 c and 3930 d that are arranged in series. Each VOA selectivelyattenuates light that originally passed through one of the respectivewaveguides 3918 a to 3918 d. The number of variable optical attenuators3930 a to 3930 d in the variable optical attenuator bank 3910,corresponds to the number of light bands that are being monitored overthe waveguides 3918 a to 3918 d. If the signal strength of one certainlight band is stronger than another light band, e.g., assume that thelight signal travelling through waveguide 3918 a is stronger than thelight signal travelling through 3918 b, then the stronger opticalsignals will be attenuated by the desired attenuation level by thecorresponding attenuator. Such attenuation makes the strength of eachoptical signal substantially uniform.

As such, all of the signal strengths on the downstream side of thevariable optical attenuators 3930 a, 3930 b, 3930 c and 3930 d should besubstantially equal, and are fed into a wavelength signal combiner 3912,where all the signals are recombined into a single signal. The opticalsignal downstream of the wavelength combiner 3912, therefore, is gainequalized (and may be considered as gain flattened). The signaldownstream of the wavelength combiner 3912 may still be relatively weakdue to a faint original signal or the relative attenuation of eachwavelength by the variable optical attenuator. Therefore, the signal isinput into the amplifier 3914. The amplifier, that is one embodiment isan Erbium Doped Fiber Amplifier (EDFA), amplifies the strength of thesignal uniformly across the different bandwidths (at least from λ₁ toλ_(n)) to a level where it can be transmitted to the next dynamic gainequalizer some distance down output waveguide 3932. Using thisembodiment, optical signals can be modulated without being convertedinto, and from, corresponding electrical signals. The variable opticalattenuators 3930 a to 3930 d and the wave length combiner 3912 can beproduced and operated using the techniques described above relating tothe optical waveguide devices.

FIG. 40 shows another embodiment of a dynamic gain equalizer 4000. Thebeam splitter 4003 and the monitor 4006 are components in the FIG. 40embodiment of dynamic gain equalizer 4000 that are located differentlythan in the FIG. 39 embodiment of dynamic gain equalizer 3900. The beamsplitter 4004 is located between the variable optical attenuator (VOA)bank 3910 and the wavelength combiner 3912. The wavelength combiner 3912may be fashioned as an arrayed waveguide (AWG) as shown in theembodiment of FIG. 34 (in a wavelength multiplexing orientation). Thebeam splitter 4004 is preferably configured to reflect a relativelysmall amount of light from each of the respective VOAs 3930 a, 3930 b,3930 c, and 3930 d. The beam splitter 4004 is configured to reflect aprescribed percentage of the light it receives from each of the VOAs3930 a to 3930 d to be transmitted to the monitor 4006. The monitor 4006converts the received light signals which relate to the strength of theindividual light outputs from the VOAs 3930 a to 3930 d into a signalwhich is input to the controller 201. The controller 201, whichpreferably is configured as a digital computer, an application specificintegrated-circuit, or perhaps even an on chip controller, determinesthe strengths of the output signals from each of the respective VOAs3930 a to 3930 d and balances the signal strengths by selectiveattenuation. For example, assume that the output signal of VOA2 3930 bis stronger than that of VOA3 3930 c, as well as the rest of the VOAs. Asignal attenuator would be actuated to attenuate the VOA2 3930 b signalappropriately. As such, the controller 201 selectively controls theattenuation levels of the individual VOAs 3930 a to 3930 d.

Each output light beam from VOAs 3930 a to 3930 d that continuesstraight through the beam splitter 4004 is received by the wavelengthcombiner 3912, and is combined into a light signal that contains all thedifferent wavelength signals from the combined VOAs 3930 a to 3930 d.The output of the wavelength 3912 is input into the amplifier, and theamplifier amplifies the signal uniformly to a level wherein it can betransmitted along a transmission waveguide to, for example, the nextdynamic gain equalizer 4000.

4C. Self Aligning Modulator

The FIG. 47 embodiment of self-aligning modulator 4700 is another systemthat performs an optical function that may include a plurality ofoptical waveguide devices. The self-aligning modulator 4700 includes aninput light coupler 4702, a first deflector 4704, a second deflector4706, an input two dimensional lens 4708 (shown as a Bragg grating typelens), a modulator 4710, an output two dimensional lens 4712 (shown as aBragg grating type lens), an output light coupler 4716, and thecontroller 201.

The input light coupler 4702 acts to receive input light that is to bemodulated by the self-aligning modulator 4700, and may be provided byany type of optical coupler such as an optical prism. The firstdeflector 4704 and the second deflector 4706 are directed to operate inopposed lateral directions relative to the flow of light through theself-aligning modulator 4700. The input two dimensional lens 4708 actsto focus light that it receives from the deflectors 4704 and 4706 so thelight can be directed at the modulator 4710. The modulator 4710modulates light in the same manner as described above. The modulator maybe formed as one of the optical waveguide devices shown in FIGS. 1-3, 4,and 5. The deflected light applied to the modulator 4710 is both alignedwith the modulator and focused. The output two-dimensional lens 4712receives light output from the modulator 4710, and focuses the lightinto a substantially parallel path so that non-dispersed light can bedirected to the output prism 4716. The output light coupler 4716receives light from the output two-dimensional lens 4712, and transfersthe light to the outside of the self-aligning modulator 4700. Thecontroller 201 may be, e.g., a microprocessor formed on a substrate4720. The controller 201 controls the operation of all the activeoptical waveguide devices 4704, 4706, 4708, 4710, and 4712 included onthe self-aligning modulator 4700.

While the modulator 4710 and the two-dimensional lenses 4008, 4012 areshown as active optical waveguide devices, it is envisioned that one ormore passive devices may be substituted while remaining within the scopeof the present invention. The two-dimensional lenses 4008, 4012 areoptional, and the self-aligning modulator will operate with one or noneof these lenses. During operation, the first deflector 4704 and thesecond deflector 4706 are adjusted to get the maximum output lightstrength through the output prism 4716.

The self-aligning modulator 4700 ensures that a maximum, or specifiedlevel, amount of light applied to the input prism 4702 is modulated bythe modulator 4710 and released to the output prism 4716. Theperformance of the self-aligning modulator system 4700 can also bechecked simultaneously. For instance, if light exiting from the outputprism is reduced, the deflectors, the lenses, and the monitor may eachbe individually varied to determine whether it causes any improvement inoperation. Other suitable control techniques and algorithms may be usedto derive an optimal operation. FIGS. 47, 48, and 49 further demonstratehow a variety of optical waveguide devices may be located on a singlesubstrate or chip.

One or more optical waveguide devices may be configured as amulti-function optical bench that facilitates alignments of a laser tothe fiber. In the optical bench configuration, that is structuredsimilarly to the FIG. 47 embodiment of the self-aligning modulator 4700,a plurality of the FIGS. 1 to 3, 4, or 5 embodiments of opticalwaveguide devices are integrated on the substrate. For example, awaveguide can be formed in the substrate so that only the gateelectrode, the first body contact electrode, the second body contactelectrode, and the electrical insulator layer have to be affixed to thesubstrate to form the FET portion. The corresponding FET portions areattached to the substrate (the substrate includes the waveguide). Assuch, it is very easy to produce a wide variety of optical waveguidedevices.

4D. Optical Systems Using Delay Components

FIGS. 48 and 49 show several embodiments of systems that my beconstructed using one or more of the embodiments of programmable delaygenerator 4200 shown in FIGS. 42 and 43. FIGS. 48 shows one embodimentof a polarization controller. FIG. 49 shows one embodiment ofinterferometer.

Polarization control is a method used to limit interference between aplurality of different polarizations that occur, for example, when lightis transmitted in a fiber for a large distance such as 3,000 kilometersor more. Light that is to be transmitted over the fiber is often splitinto two polarizations, referred to as P polarization and Spolarization. The polarization is received at the other end of the fiberin some arbitrary polarization state since the fiber may encounterdifferent propagation constants for the P polarization signal and the Spolarization signal. Therefore, the P polarization signal and the Spolarization signal may be modulated within the fiber differently, andmay travel at different rates, and may be attenuated differently. Forexample, the duration between a first polarization and a secondpolarization may extend from a duration indicated as d to a longerduration shown as d′ as the signal is transmitted over a longtransmission fiber. When multiple data bits are transmitted, the Ppolarization signal and the S polarization signal for adjacent bits mayoverlap due to the different velocities of the polarizations. Forexample, one polarization of the previous bit is overlapping with theother polarization of the next bit. If a network exceeds a hundredpicoseconds at 10 gigahertz, there is a large potential for suchoverlap. An example of such a network is Network Simplement, nextgeneration network presently under development in France.

The embodiment of polarization controller 4800 shown in FIG. 48comprises a transmission fiber 4802, an output 4804, an adjustablepolarizer 4806, a beamsplitter 4808, a first path 4810, a second path4812, and a combiner 4813 that combines the first path and the secondpath. The first path 4810 includes a programmable delay generator 4814.The second path 4812 comprises a programmable delay generator 4816. Thetransmission fiber 4802 may be fashioned as a channel waveguide oroptical fiber. The adjustable polarizer 4806 may be fashioned as a slabwaveguide. The beamsplitter 4808 may be fashioned as the beamsplitter4600 shown and described relative to FIG. 46. The combiner 4813 may befashioned as the arrayed waveguide (AWG) shown and described relative toFIG. 34 configured as a multiplexer. The programmable delayed generators4814 and 4816 may be fashioned as the embodiment of programmable delaygenerator 4200 shown and described relative to FIG. 42.

During operation, light travelling down the transmission fiber 4802 maybe formed from a plurality of temporarily spaced data bits, with eachdata bit having a P polarization and an S polarization. The temporalseparation between a first polarization and a second polarization mayseparate from a distance shown as d to a distance shown as d′.Approximately every couple thousand miles, or as determined suitable forthat particular transmission system, one polarization controller 4800can be located within the transmission system to limit any adverseoverlapping of polarizations.

The polarization controller 4800 acts to adjust the temporal spacing ofeach signal, and therefor limits the potential that the time betweenadjacent polarizations from adjacent signals is reduced to thepolarizations are in danger of overlapping. As such, as the opticalsignal is received at the output 4804 of the transmission fiber 4802, itencounters the polarizer 4806 that separates the polarized signals.After the polarized signals are cleanly separated, the signal continueson to the beamsplitter. The beamsplitter 4808 splits the signal into twopolarizations, such that a first polarization follows the first path4810 and the second polarization follows a second path 4812. Theprogrammable delay generators 4814 and 4816 are included respectively inthe first path 4810 and the second path 4812 to temporally space therespective first polarization (of the P or S variety) and the secondpolarization (of the opposed variety) by a desired and controllableperiod. Providing a temporal delay in the suitable programmable delaygenerator 4814, 4816 allows the controller 201 to adjust the temporalspacing between the P polarization and the S polarization by aprescribed time period, as dictated by the operating conditions of thenetwork. It is common in long data transmission system to have the Ppolarization and the S polarization temporally separate further apart.The polarization controller 4800 readjusts the time between the Spolarization and the P polarization. As such, the S polarization or theP polarization will not overlap with the polarizations from adjacentsignals.

For a given fiber, each color has its own polarization controller 4800.There might be 80 colors being used in a typical optical fiber, so therehave to be a large number of distinct polarization controllers to handleall the colors in a fiber. A central office for a telephone network maybe terminating a large number of fibers (e.g., 100). As such, a centraloffice may need 8000 polarization controllers at a central office todeal with the dispersion problem on all of their fibers. As such,expense and effectiveness of operation of each polarization controllerare important.

FIG. 50 shows one embodiment of a method 5000 that can performed by thecontroller 201 in maintaining the temporal separation of a firstpolarization and a second polarization between and input optical signaland an output optical system. The method 5000 starts with block 5002 inwhich the controller detects the first temporal separation of a firstpolarization and a second polarization in the output optical signal. Theoutput optical signal may be considered to be that signal which isapplied to the input 4804 in FIG. 48, as referenced by the character d′.

The method 5000 continues to block 5004 in which the controller 201compares the first temporal separation of the output optical signal to asecond temporal separation of an input optical signal. The input opticalsignal is that signal which is initially applied to the transmissionfiber, and is indicated by the referenced character d in FIG. 48. Thecontroller 201 typically stores, or can determine, the value of thesecond temporal separation between the first polarization and the secondpolarization. For example, a transmitter, or transmission system, thatgenerates the signal using two polarizations may typically provide afixed delay d between all first polarizations and the correspondingsecond polarizations in the input optical signal. Alternatively, thecontroller 201 may sense whether the temporal separation distance d′between first polarization and the second polarization of the outputoptical signal are becoming too far apart. In both cases it is desiredto reduce the second temporal separation.

The method 5000 continues to step 5006 in which the controller 201separates the input optical signal into two paths, indicated as thefirst path 4810 and the second path 4812 in FIG. 48. The separated firstpolarization from the output optical signal is transmitted along thefirst path 4810. The separated second polarization from the outputoptical signal is transmitted along the second path 4812.

The method continues to step 5008 in which the controller, using eitherthe first programmable delay generator 4814 or the second programmabledelay generator 4816 that are located respectively in the first path4810 and the second path 4812, delay the light flowing through theirrespective paths. Such a delay of the light along each respective path4810, 4812 corresponds to the respective first polarization or thesecond polarization travelling through each respective path. Oneembodiment of the delay of the light in the respective programmabledelay generators 4814, 4816 is provided in a similar matter to asdescribed in the embodiments of programmable delay generator 4200 shownin FIGS. 42 and 43. The method 5000 continues to block 5010 in which thefirst polarization that travels over the first path 4810 and the secondpolarization that travels over the second path 4812 are combined (andinclude the respective delays for each polarization). Combining thesesignals form an output optical signal having its temporal spacingbetween the first polarization and the second polarization modified.This output optical signal having modified temporal spacing may be inputas an input optical signal to a new length of transmission fiber, or maybe transmitted to the end user.

FIG. 49 shows one embodiment of an interferometer that may beconstructed using optical waveguide devices, including one or moreprogrammable delay generators 4200. The interferometer 4900 (e.g., aMichelson interferometer) comprises a laser 4902, a beamsplitter 4904, afirst programmable delay generator 4906, a second programmable delaygenerator 4908, and an interference detector 4910. In the interferometer4900, one or both of the first programmable delay generator 4906 and thesecond programmable delay generator 4908 must be provided. If only oneof the two programmable delay generators is provided, then a mirror issubstituted at the location of the missing programmable delay generator.

During operation, coherent light is applied from the laser 4902. Thecoherent light, follows path 4920 and encounters the beamsplitter 4904.The beamsplitter splits the coherent light from the laser into to followeither path 4922 or path 4924. Light following path 4922 will encounterthe first programmable delay generator 4906 and will be reflected backtoward the beamsplitter. Light following path 4924 will encounter thesecond programmable delay generator 4908 and will be reflected backtoward the beamsplitter 4904. As a return path of light from travellingalong path 4924 and 4922 encounters the beamsplitter, a certainproportion of the return light following both paths 4924 and 4922 willbe reflected to follow path 4926.

Based upon the position of the first and second programmable delaygenerators 4906, 4908, the light travelling along paths 4922 and 4924will travel a different distance (the distances traveled include theoriginal path and the return path from the programmable delaygenerator). These differences in distances will be indicated by theinterference pattern in the signal following path 4926. Depending on thewavelength of light used in the Michelson interferometer, the Michelsoninterferometer may be used to measure differences in distance betweenpath 4922 and 4924. In one embodiment, one or more of the programmabledelay generator shown as 4906, 4908 is replaced by a mirror or a likedevice. For example, a modified Michelson interferometer may be used asin optical interference topography in which the position of the retina,relative to the eye, is measured to determine the state of the eye. Theretina acts as a mirror, and focuses some of the light out of the eye.Therefore, an interferometer, or more specifically an opticalinterference topography device can detect light reflected off theretina. As such, in the Michelson interferometer, one of theprogrammable delay generators 4906 or 4908 can be replaced by the eye ofthe examined patient. The other one of the programmable delay generators4908, 4906 can be used to measure distances within the eye.

The embodiment of the methods shown in FIGS. 7 and 8 may be used toadjust or calibrate the voltage applied to an electrode of an opticalwaveguide devices based on variations in such parameters as device ageand temperature. These methods rely on such inputs as the temperaturesensor 240 measuring the temperature of the optical waveguide device andthe meter 205 measuring the resistance of the gate electrode, as well asthe controller 201 controlling the operation of the optical waveguidedevice and controlling the methods performed by FIGS. 7 and 8. Themethods may be applied to systems including a large number of opticalwaveguide devices as well as to a single optical waveguide device. Assuch, the optical waveguide system, in general, is highly stable andhighly scalable.

While the principles of the invention have been described above inconnection with the specific apparatus and associated method, it is tobe clearly understood that this description is made only by way ofexample and not as a limitation on the scope of the invention.

1. An optical lens that generates a focused output optical signal,comprising: a waveguide that includes an input port wherein the inputoptical signal is introduced into the waveguide, an output port whereinthe focused output optical signal exits the waveguide, and a region offocusing propagation constant disposed along a length of the waveguideand between the input port and the output port, wherein the inputoptical signal is guided by total internal reflection in the waveguide,and the waveguide is formed at least in part from an activesemiconductor; a first electrode positioned proximate a first surface ofthe region of focusing propagation constant and electrically separatedfrom the active semiconductor; a second electrode in electrical contactwith the active semiconductor and disposed on a first side of the regionof focusing propagation constant; a two-dimensional electron (hole) gas(2DEG) having a free carrier distribution that is formed on the firstsurface when a voltage is applied between the first electrode and thesecond electrode; and wherein changing the voltage causes acorresponding change of the free carrier distribution which, in turn,causes corresponding change of a propagation constant level in theregion of focusing propagation constant and adjustment of a focal lengthof the optical lens.
 2. The optical lens of claim 1, further comprisinga third electrode in electrical contact with the active semiconductordisposed on a second side of the region of focusing propagation constantopposite the first side; wherein the second and third electrodes areelectrically coupled to a common potential.
 3. The optical lens of claim1 or 2, wherein the 2DEG is oriented in a plane that is substantiallyparallel to the region of focusing propagation constant.
 4. The opticallens of claim 2, further comprising a field effect transistor (FET)portion that includes the first, second, and third electrodes.
 5. Theoptical lens of claim 4, wherein the FET portion is from one of thegroup of metal-oxide-semiconductor FET (MOSFET), metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor field effecttransistor (MESFET), a high electron mobility transistor (HEMT), or amodulation doped FET (MODFET).
 6. The optical lens of claim 1, furthercomprising a metal oxide semiconductor capacitor (MOSCAP) portion. 7.The optical lens of claim 6, wherein the body contact electrode islocated below the waveguide.
 8. The optical lens of claim 1, wherein thewaveguide comprises any group III or group V semiconductor.
 9. Theoptical lens of claim 1, wherein the free-carrier distribution of the2DEG layer is varied by changing the voltage applied to the firstelectrode, and wherein light flowing through the waveguide iscontrollably attenuated in response to the voltage applied to the firstelectrode.
 10. An optical lens having a focal length that varies bychanging a propagation constant level of a region of focusingpropagation constant of a waveguide, comprising: a gate electrode havinga prescribed electrode shape positioned proximate the waveguide; avoltage source connected to the gate electrode for applying voltage tothe gate electrode, wherein the voltage causes the gate electrode toproject into the waveguide the region of focusing propagation constant,said region of focusing propagation constant corresponding generally inshape to the prescribed electrode shape and focusing light flowingthrough the waveguide; and a controller that controls the propagationconstant level of the region of focusing propagation constant and thefocal length by varying the voltage applied to the gate electrode toadjustably focus light flowing through the waveguide.
 11. The opticallens of claim 10, wherein the 2DEG is oriented in a plane that issubstantially parallel to the region of focusing propagation constant.12. The optical lens of claim 10, further comprising a field effecttransistor (FET) portion including a source electrode and a drainelectrode.
 13. The optical lens of claim 10, wherein the FET is from oneof the group of metal-oxide-semiconductor FET (MOSFET), metal-electricalinsulator-semiconductor FET (MISFET), a metal semiconductor field effecttransistor (MESFET), a high electron mobility transistor (HEMT), or amodulation doped FET (MODFET).
 14. The optical lens of claim 10, furthercomprising one or more body contact electrode(s) positioned relative tothe waveguide and electrically integrated with the active semiconductor.15. The optical lens of claim 14, further comprising a metal oxidesemiconductor capacitor (MOSCAP) portion that includes the body contactelectrode.
 16. The optical lens of claim 14, wherein the body contactelectrode is located below the waveguide.
 17. The optical lens of claim14, wherein the body contact electrode includes a first body contactelectrode and a second body contact electrode, the first body contactelectrode, the gate electrode, and the second body contact electrode arelocated above the waveguide.
 18. The optical lens of claim 17, whereinthe first body contact electrode is located on an opposed side of thegate electrode from the second body contact electrode, and wherein thewaveguide comprises any group III or group V semiconductor.
 19. Theoptical lens of claim 10, wherein the free-carrier distribution of the2DEG layer is varied by changing the voltage applied to the gateelectrode, and wherein light flowing through the waveguide iscontrollably attenuated in response to the voltage applied to the gateelectrode.
 20. The optical lens of claim 10, further comprising anoptical device coupled with a variable coupling to the optical lens. 21.A method for focusing light by changing a propagation constant level ofa region of focusing propagation constant of a waveguide in an opticaldevice, the method comprising: positioning a planar electrode proximatethe waveguide; applying a voltage to the planar electrode to change thelevel of propagation constant in the region of focusing propagationconstant in the waveguide wherein the region of focusing propagationconstant corresponds in shape to the planar electrode shape; andcontrolling a propagation constant level of the region of focusingpropagation constant and the focal length of the device by varying thevoltage to control the focusing of light flowing in the waveguide. 22.The method of claim 21, further comprising a 2DEG located between theplanar electrode and the body contact electrode, wherein the 2DEG isoriented in a plane that is substantially parallel to a length of theregion of focusing propagation constant.
 23. The method of claim 21,further comprising a field effect transistor (FET) portion including aplanar electrode.
 24. The method of claim 21, wherein the FET is fromone of the group of metal-oxide-semiconductor FET (MOSFET),metal-electrical insulator-semiconductor FET (MISFET), a metalsemiconductor field effect transistor (MESFET), a high electron mobilitytransistor (HEMT), or a modulation doped FET (MODFET).
 25. The method ofclaim 21, further comprising one or more body contact electrode(s)positioned relative to the waveguide and electrically integrated withthe active semiconductor.
 26. The method of claim 21, further comprisinga metal oxide semiconductor capacitor (MOSCAP) portion including thebody contact electrode.
 27. The method of claim 26, wherein the bodycontact electrode is positioned below the waveguide.
 28. The method ofclaim 26, wherein the body contact electrode includes a first bodycontact electrode and a second body contact electrode, the first bodycontact electrode, the planar electrode, and the second body contactelectrode are located above the waveguide; and the first body contactelectrode is located on an opposed side of the planar electrode from thesecond body contact electrode.
 29. The method of claim 21, wherein thewaveguide comprises any group III or group V semiconductor.
 30. Themethod of claim 21, wherein the free-carrier distribution of the 2DEGlayer is changed by changing the voltage applied to the planarelectrode, and wherein light flowing through the waveguide iscontrollably changed in response to changing the free-carrierdistribution of the 2DEG layer.
 31. The method of claim 21, furthercomprising an optical device coupled with a variable coupling to theoptical lens.
 32. An optical lens for focusing light flowing through awaveguide by changing the propagation constant level of the waveguide,the optical lens comprising: a region of focusing propagation constantdisposed along a length of the waveguide and defining a region wherelight is focused, wherein the light is guided within the waveguide bytotal internal reflection, and the waveguide is formed at least in partfrom an active semiconductor; a Field Effect Transistor portion (FETportion) including a gate electrode, a source electrode, and a drainelectrode; the gate electrode is mounted to, but electrically insulatedfrom, the active semiconductor; the drain electrode and the sourceelectrode are held at a substantially common voltage; wherein the gateelectrode, the source electrode, and the drain electrode are positionedsubstantially above the waveguide, the source electrode is located on asubstantially opposed side of the gate electrode from the drainelectrode; a two-dimensional electron (hole) gas (2DEG) forming a layerhaving a free carrier distribution that is formed on a first surface ofthe waveguide when a voltage is applied between the gate electrode andthe common voltage; a voltage source connected to the gate electrode forapplying the voltage to the gate electrode, wherein the gate electrodeprojects the region of focusing propagation constant into the waveguideto focus light flowing through the waveguide; and a controller forcontrolling the propagation constant level of the region of focusingpropagation constant and a focal length of the lens by varying thevoltage produced by the voltage source to control the focusing of lightflowing within the waveguide.
 33. An apparatus for focusing an inputoptical signal in order to generate a focused output optical signal,comprising: a planar electrode positioned proximate the waveguide; meansfor generating a region of focusing propagation constant in thewaveguide that substantially corresponds in shape to a shape of theplanar electrode, by applying a voltage to the planar electrode; andmeans for controlling a propagation constant level of the region offocusing propagation constant and a focal length by varying the voltageto control the focusing of light flowing through the waveguide.
 34. Amethod for generating a focused output optical signal by passing aninput optical signal through a waveguide, comprising: providing a gateelectrode proximate the waveguide; providing a body contact electrodeproximate the waveguide; applying the input optical signal to thewaveguide; applying a voltage to the gate electrode that generates aregion of focusing propagation constant in the waveguide; and generatingthe focused output optical signal at a focal point that varies inresponse to variations of the voltage.